Question

If I can paint a wall in 20 min and my friend can paint a wall in 30 min. How many minutes would it take for us to paint a wall working together.

Answer 1

Answer: $12\ \text{min}$

Step-by-step explanation:

Given

It takes 20 min and 30 min for  a person and his friend to paint a wall individually  i.e.

In 1 min they cover $\frac{1}{20}$ part and $\frac{1}{30}$ part of wall respectively.

If the work together, 1 minute work is

$\Rightarrow \dfrac{1}{20}+\dfrac{1}{30}\\\\\Rightarrow \dfrac{3+2}{60}\\\\\Rightarrow \dfrac{5}{60}$

Time required will be reciprocal of it

$\Rightarrow \dfrac{60}{5}=12\ \text{min}$