lmuenzel wrote:

On a journey across Dhaka, a bus averages 10 miles/h for 20% of the distance, 30 miles/h for 60% of it and 20 miles/h for the remainder. What is the average speed for the whole journey?

(A) 10mph

(B) 30mph

(C) 5 mph

(D) 20 mph

(E) 25 mph

Avg. speed = total distance/ total time

Let total distance be X

As distance is divided into three parts 20% , 60% and again 20%

means distance of three part journey will be 20% of X = 20X/100 =X/5

and 60% of X = 60X/100 = 3x/5

avg speed = X / (x/(5*10) + x/ (3X/5*30) + X/ (5*20))

taking x common from dinominator and cancelling

we get Avg. speed =20mph

Ans D