How to compute Stock Dividend
Stock or scrip dividends are those paid out in the form of additional stock shares of the issuing corporation, or another corporation (such as its subsidiary corporation). They are usually issued in proportion to shares owned (for example, for every 100 shares of stock owned, a 5% stock dividend will yield 5 extra shares). If the payment involves the issue of new shares, it is similar to a stock split in that it increases the total number of shares while lowering the price of each share without changing the market capitalization, or total value, of the shares held. (http://en.wikipedia.org/wiki/Dividend)
In this case you can derive the New number of shares by this formula:
new average price = previous average * previous no. of share / new no. of shares