Question

The speed of the motorboat in still water if a motorboat travels 30 minutes upstream against 4mphcurrent. Returning with the current takes 18 minutes.a)14 mphb) 15 mphc)16 mphd)17 mph​

Answer 1

Answer:

Let, speed of motorboat in still water is k mph

Then for upstream rate is (k-4) mph & for returning rate is (k+4) mph.

So, for going in 30 minutes it goes 30(k-4)/60 mile = (k-4)/2 mile

For returning in 18 minutes it goes 18(k+4)/60 mile = 3(k+4)/10 mile

Accordingly , (k-4)/2 = 3(k+4)/10

Or, 10k - 40 = 6k + 24

Or, 4k = 64

Or, k = 16

So, speed of motorboat in still water is 16 mph.

So, rate in upstream is 12 mph and downstream is 20 mph.

Upstream take 30 minutes and downstream takes 18 minutes

Both cover the distance 6 mile. ( By putting k value in upstreams and downstream goes distance).