Question

27 students in all 4:5 packed lunch. how many students packed lunch

Answer 1

$\bf \stackrel{total}{27}\qquad 4:5\qquad \cfrac{4}{5}\implies \cfrac{4\cdot \frac{27}{4+5}}{5\cdot \frac{27}{4+5}}\implies \cfrac{4\cdot 3}{5\cdot 3}\implies \cfrac{\stackrel{packed~lunch}{12}}{\stackrel{did~not~pack~lunch}{15}}$