Lalremsiami must average 60 km/h over a 240 km drive. She covers the first 120 km at 40 km/h. At what speed must she drive the remaining 120 km?

Explanation

1. 01

   To average 60 km/h over 240 km she has $\frac{240}{60} = 4$ h in all.

2. 02

   The first 120 km at 40 km/h uses $\frac{120}{40} = 3$ h.

3. 03

   She has 1 h left for 120 km, so she needs 120 km/h.