Ramu works 4 times as fast as Somu. If Somu can complete a work in 20 days independently, then the number of days in which Ramu and Somu together can complete the work is:

Number of days required for Somu to complete work = 20 days

Ramu works 4 times as fast as Somu

$$=$$> Number of days required for Ramu to complete work = $$\frac{20}{4}=5$$ days

Let the Total Work = W

Work done by Ramu in 1 day = $$\frac{W}{5}$$

Work done by Somu in 1 day = $$\frac{W}{20}$$

Work done by Ramu and Somu in 1 day = $$\frac{W}{5}+\frac{W}{20}=\frac{5W}{20}=\frac{W}{4}$$

Number of days required for both Ramu and Somu together to complete work = $$\frac{W}{\frac{W}{4}}=4$$ days

Hence, the correct answer is Option A