Question

A bathtub is being filled with water. After 3 minutes 4/5 of the tub is full. Assuming the rate is constant, how much longer will it take to fill the tub?

Answer 1

$3\ min - \frac45\\ x\ min - 1\\ \\ 3=\frac45 x\ /:\frac45\\ \frac{3}{\frac45}=x\\ x=3\cdot \frac54=\frac{15}4=3\frac34\ min=3\ min\ 45\ s$

Answer 2

$3\ min\ ----->\frac45\\x\ min\ ----->1\\x\ \cdot\ \frac45=1\cdot3\\\frac45x=3\ /\ : \frac45\\x=3\ :\ \frac45\\x=\frac31\ \cdot\ \frac54\\x=\frac{15}{4}\\x=3\frac34\ [min]\\x=3\ min\ 45\ sec$

answer: 3 min 45 sec