

View Answer
Shortcut:
If a certin distance is covered at a km/hr and the same distance is covered at b km/hr then the average speed during the whole journey is
2ab
/
a + b
km/hr.
Here, a = 64, b = ?
Using these values in the shortcut, we get:
Average speed =
2 x 64 x b
/
64 + b
56 =
2 x 64 x b
/
64 + b
56(64 + b) = 2 x 64 x b
7(64 + b) = 16b
16b − 7b = 448
9b = 448
b =
448
/
9
= 49.777 or 50 (round off)
Hence, the return speed is 50 km/hr.

