Rosa can eat 32 rosogollas in one hour. Her sister Lila needs three hours to eat the same number. How much time will they take to eat 32 rosogollas together ?

Answer: Option A

Number of rosogollas eaten by Rosa in 1 minute = $$\frac{32}{60}$$
Number of rosogollas eaten by Lila in 1 minute =$$\frac{32}{180}$$
Number of rosogollas eaten by Rosa and Lila together in 1 minute
$$\begin{array}{rl}& \text{ = }\left(\frac{32}{60}+\frac{32}{180}\right)\\ & \text{ = }\frac{128}{180}\\ & \therefore \text{Required time}\\ & =\left(32÷\frac{128}{180}\right)\text{minutes}\\ & =\left(\frac{32\times 180}{128}\right)\text{minutes}\\ & =\text{ 45 minutes}\end{array}$$