SAT Mathematics Practice Test 4

In the study, $240$ male and $160$ plus another $100$ female bats have been tagged, so that 500 bats have been tagged altogether. If $\mathit{x}$ more male bats must be tagged for $\frac{3}{5}$ of the total number of bats to be male, the proportion must be true. Multiplying each side of $\frac{240+\mathit{x}}{500+\mathit{x}}=\frac{3}{5}$ by $5\left(500+\mathit{x}\right)$ gives $5\left(240+\mathit{x}\right)=3\left(500+\mathit{x}\right)$ which simplifies to $1200+5\mathit{x}=1500+3\mathit{x}.$ Therefore,$\mathit{x}=150$,and $150$ more male bats must be tagged; this will bring the total to $390$ male bats out of $650$ bats, which is equal to $\frac{3}{5}$