Advertisement

### Question

An airplane can travel at $3{1/5}$ km/h in still air. But it takes thrice as much time to travel upstream as compared to the time it takes downstream, if air is blowing at a rate of R km/h. What is R?

**A**

$1{3/5}$ km/h.

**B**

$3{1/4}$ km/h.

**C**

${3/7}$ km/h.

**D**

$3{2/7}$ km/h.

**Soln.**

**Ans: a**

If the distance travelled is D, we have $D/{16/5 - R}$ = 3 × $D/{16/5 + R}$. Cancelling D, and solving for R, we get R = ${8/5}$, which is same as: $1{3/5}$ km/h.