Question

a/30=b/15=2/5
a*b-7=?

Answer 1

$\rm \boxed{\rm \frac{a}{30}= \frac{b}{15}}= \frac{2}{5} \\ \\ 15a=30b|:15 \\ a=2b \\ \\ \frac{a}{30}= \boxed{\rm \frac{b}{15}= \frac{2}{5}} \\ \\ 5b=30|:5 \\ \bold{b=6} \\ \\ a=2\cdot 6 \\ \bold{a=12} \\ \\ 6\cdot12-7= \\ 72-7= \bold{65}$