Example $2$: Weighted average number of shares outstanding On January $1,2020,$ Chang Corp. had $450,000$ shares of common stock outstanding. During $2020,$ it had the following transactions that affected the common stock account February $1$Issued $150,000$ Shares April $1$ May $1$ June $1$ Issued a $10\%$ stock dividend Acquired $90,000$ share of treasury stock Issued a $2-$for $-1$ stock split October $1$Reissued $60,000$ shares of treasury stock Determine the weighted$-$average number of shares outstanding as of December $31,2020.$