Defendant assigns error to the trial court’s classification of the Camp Branch Road property, the office building, the Buie note and the Eagles Nest stock. He also assigns error to the valuation of his law practice and to the order that he repay plaintiff for the payments he collected under the Medford note after separation. Finally, defendant contends the trial court erred by distributing personal property listed in a handwritten memorandum signed by the parties, but not acknowledged before a certifying officer, in April 1984.
Defendant’s first contention is that “[t]he court erred in failing to make appropriate findings of fact, conclusions of law, and orders that the defendant’s separate inherited funds which were invested in the Camp Branch Road property and in the office building remained the separate property of the defendant.” He also argues that “[t]he trial court erred by requiring the defendant to present clear, cogent and convincing evidence to rebut the presumption of gift utilized by the trial court in regard to the Camp Branch Road property [and] office building.” We disagree.
It is true that there may be both marital and separate ownership interests in the same property. Wade v. Wade, 72 N.C. App. 372, 325 S.E. 2d 260, disc. rev. denied, 313 N.C. 612, 330 S.E. 2d 616 (1985). Our courts have adopted a source of funds approach to distinguish marital and separate contributions to a single asset. Id. Under the source of funds approach, each party retains as *289separate property the amount he contributed to purchase the property plus passive appreciation in value. Id. Thus, defendant contends the contributions from his inherited funds to the purchase price of the home and office building remain his separate property. However, “where a spouse furnishing consideration from separate property causes property to be conveyed to the other spouse in the form of tenancy by the entireties, a presumption of a gift of separate property to the marital estate arises, which is rebuttable by clear, cogent, and convincing evidence.” McLeod v. McLeod, 74 N.C. App. 144, 154, 327 S.E. 2d 910, 916-17, cert. denied, 314 N.C. 331, 333 S.E. 2d 488 (1985). By placing title to the properties in both names as tenants by the entirety, defendant is presumed to have made a gift of his separate property to the marital estate.
 Defendant argues that the presumption of marital gift for entireties property is no longer valid in this State and that the court erred by requiring him to present clear, cogent, and convincing evidence that he intended to retain a separate interest in the property. Defendant cites Johnson v. Johnson, 317 N.C. 437, 346 S.E. 2d 430 (1986), and Dunlap v. Dunlap, 85 N.C. App. 324, 354 S.E. 2d 734 (1987) as authority for his position. In Dunlap, this Court stated that a footnote in Johnson overruled a presumption stated in McLeod that all property acquired by the parties during the marriage is marital property. Id. at 328, 354 S.E. 2d at 736. The issue before us, however, is not whether all the property acquired during the marriage is presumed to be marital property, but whether the use of separate property to acquire property, title to which is taken as tenants by the entirety, creates a presumption of a gift to the marital estate. As neither Johnson nor Dunlap disturbed the presumption on this issue stated in McLeod, we hold that the trial court properly applied the presumption of a gift to the marital estate in this case.
 Defendant next contends that if the trial court was correct in applying the presumption of gift to the marital estate and in requiring him to present clear, cogent, ¿nd convincing evidence to rebut the presumption, then the court erred in finding he had not met his burden of proof. Defendant presented evidence showing the source of his separate funds and their application to the Camp Branch Road property and the office building. He also elicited testimony from plaintiff that she did not want to be awarded any*290thing from defendant’s inheritance. Whether defendant succeeded in rebutting the presumption of gift to the marital estate by clear, cogent, and convincing evidence is a matter left to the trial court’s discretion. Defendant’s evidence “may be clear and cogent, but evidently it was not convincing to the trial court.” Draughon v. Draughon, 82 N.C. App. 738, 739, 347 S.E. 2d 871, 872 (1986), cert. denied, 319 N.C. 103, 353 S.E. 2d 107 (1987). There is some competent evidence to support the trial court’s findings; therefore, its rulings will not be disturbed on appeal. Lawing v. Lawing, 81 N.C. App. 159, 344 S.E. 2d 100 (1986). These assignments of error are overruled.
 Defendant next contends the trial court erred in classifying the Buie note as marital property. He contends that even though both parties’ names were on the note, the note remained his separate property. We agree with defendant that the Buie note is his separate property.
The presumption of gift created by the holding in McLeod was limited in its application to real property acquired by both spouses, as tenants by the entirety, in exchange for the separate property of one of them. We decline to extend that presumption to jointly held personal property which is acquired in exchange for the separate property of one spouse, as to do so would seem to defeat the legislative intent of G.S. 50-20(b)(2).
Manes v. Harrison-Manes, 79 N.C. App. 170, 172, 338 S.E. 2d 815, 816 (1986). Separate property remains separate property when it is exchanged for other separate property unless the conveyance states a contrary intention. G.S. 50-20(b)(2). The record discloses no evidence of such a contrary intent with respect to the Buie note. Even though both names are on the note, that fact alone is not sufficient to show an intent to make a gift to the marital estate. Manes, supra. The Buie note, property acquired in exchange for defendant’s separate property, remains his separate property. Thus, the court erred in distributing it as part of the equitable distribution order.
 Defendant next contends that the court erred by classifying the Eagles Nest stock as marital property. Defendant testified that the stock, issued in his name alone, was a gift from the corporation’s president, Mr. Tom Daniels, who filed a gift tax return *291with regard to the transfer. Defendant also testified that the stock was not given as payment for services to the corporation but that he continued to bill Eagles Nest for legal services. In his deposition, however, Mr. Daniels testified that while he did transfer the stock to defendant to involve defendant as an owner of the corporation, he expected defendant to be a local contact for the corporation and to perform managerial services. The corporation continued to pay defendant for his legal services, but defendant did not receive a managerial fee for his other services until he became an officer of the corporation. Mr. Daniels did not recall whether he filed a gift tax return with regard to the transfer of the stock. The court also found that both plaintiff and defendant visited the corporation’s property “to check on the property and follow the progress of various developments” on the property. The evidence is sufficient to support the trial court’s finding that the stock is marital property; therefore, its ruling will not be disturbed on appeal. Lowing, supra.
Defendant assigns as error the admission at trial of plaintiffs opinion that the value of defendant’s professional association was “at least fifty thousand dollars” on the date of separation. He does not argue this assignment of error. Thus, it is deemed abandoned. App.R. 28.
 Defendant also assigns error to the admission of the opinion of plaintiffs witness, Foster Shriner, regarding the value of defendant’s law practice. Mr. Shriner, received by the trial court as an expert, testified that the value of the professional association on the date of separation was $61,910.00. Defendant contends that this testimony should have been excluded as the witness did not “follow the prerequisites as set forth in Poore v. Poore in making a determination as to the value of this professional association.” The requirement for the admissibility of an expert’s opinion is that it “will assist the trier of fact to understand the evidence or to determine a fact in issue.” G.S. 8C-1, Rule 702. The criteria set out in Poore v. Poore, 75 N.C. App. 414, 331 S.E. 2d 266, disc. rev. denied, 314 N.C. 543, 335 S.E. 2d 316 (1985), are factors for the court to consider in valuing the professional interest and are not criteria for admissibility of the expert’s opinion. Mr. Shriner explained the methods used to reach his opinion of value, and defendant was free to, and did, cross-examine the witness regarding *292the factors set out in Poore. We find no error in the admission of this evidence.
 Defendant also argues the court’s valuation of the law practice at $35,000.00 is not supported by the evidence. “The task of the reviewing court on appeal is to determine whether the approach used by the trial court reasonably approximated the net value of the . . . interest.” Poore v. Poore, supra at 419, 331 S.E. 2d at 270. Defendant testified and offered the testimony of several local attorneys that the value of his law practice on the date of separation was around $9,000.00 to $12,000.00. Plaintiffs witness Shriner valued the practice at $61,910.00. He reached this valuation by valuing the practice’s assets and using a “multiple of earnings” approach to arrive at his figure. Based on the figure supplied by Shriner, the trial court used a “return on investment” approach to compute a value for the practice. Assuming arguendo that the “return on investment” approach is an acceptable method of valuing a professional practice, there was no evidence before the court to support the rate of return used by the court in making its calculations or to indicate that such a method would yield an accurate valuation. Therefore we must vacate the court’s findings with respect to the value of defendant’s law practice.
Defendant next excepts to the trial court’s finding of fact that he converted the money collected from the Medford note to his own use and assigns error to the court’s order that he be required to repay plaintiff the amount collected. At trial, defendant testified he used the sums collected from the Medford note to pay bills, house payments, insurance and “anything I need money for I’ll put it in the Camp Branch property.” His testimony supports the court’s finding that defendant used the money for his own purposes; that finding is, therefore, conclusive. Lawing, supra. In addition, the court’s order that defendant repay plaintiff for the amounts collected is not an abuse of its discretion and, therefore, will not be disturbed. See White v. White, 312 N.C. 770, 324 S.E. 2d 829 (1985).
[71 Defendant also assigns error to the trial court's failure to find that he had made all payments on the Camp Branch Road property from the date of separation and to its failure to credit him with the amount of those payments, which were made from his post-separation, and thus separate, property. Hunt v. Hunt, 85 *293N.C. App. 484, 355 S.E. 2d 519 (1987), requires the court to credit a former spouse “with at least the amount by which he decreased the principal owed” on marital debt by using his separate funds. Id. at 491, 355 S.E. 2d at 523. On remand, the court should enter an order crediting defendant with at least the amount by which he decreased the principal amount of the joint debt. Id.
[8J By his final assignment of error, defendant contends the trial court erred by ordering the distribution of personal property in a manner different than previously agreed in a handwritten memorandum. We disagree. G.S. 50-20(d) requires that written agreements between spouses distributing property must be “duly executed and acknowledged in accordance with . . . G.S. 52-10 and 52-10.1” in order to be binding on the parties. As the handwritten agreement was not acknowledged before a certifying officer as defined in G.S. 5240(b), it was not binding upon the court and the court was free to distribute the property. This assignment of error is overruled.
For the reasons stated, the equitable distribution judgment entered in this case is vacated. This case is remanded for a new determination of the value of defendant’s law practice, classification of the parties’ property consistently with this opinion, and entry of an appropriate order distributing that property.
Vacated and remanded.
Chief Judge HEDRICK concurs.
Judge GREENE concurs in part and dissents in part.