Question

One half of the birds at a pet store were yellow. Tara buys one. Then 1/3 of the birds left are yellow.  How many yellow birds were left at the store before Tara bought them?

Answer 1

`x-the\ number\ of\ yellow\ birds\ at\ the\ beginning,\ \ \ x>0\\ \\ (x-1)/(2x) = (1)/(3) \\ \\3\cdot(x-1)=2x\cdot1\\ \\3x-3=2x\ \ \ \Rightarrow\ \ \ 3x-2x=3\ \ \ \Rightarrow\ \ \ x=3\\ \\ Ans.\ the\ number\ of\ yellow\ birds\ at\ the\ beginning\ is\ 3`