Question

a boat can cover 28km downstream in 45 min.the ratio of speed of boat in still water ti the speed of stream is 7:3.find the difference between time taken by boat to cover 60km downstream and 40 km upstream​

Answer 1

ANSWER:

1.25 hours (approx)

Solution:

Let the speed of still water be 7x and speed of stream be 3x

Now it is given that boat cover 28km downstream in 45 minutes than speed of boat will be

→ $\frac{28}{\frac{3}{4}hours}=7x+3x$

→ $\frac{28\times 4}{3}=10x$

From here

→ x=3.7

Hence

speed of boat → 7x=25km/h

speed of stream→ 3x= 11km/h

Now find difference between time taken to travel 60km downstream and 40 km up stream

Time taken to travel 60km downstream

→ Total speed= 25+11= 36km/h

→ Distance= 60km

→ Time = 60/36=1.6Hours--------------------------(1)

Time taken to travel 40km upstream

→ Total speed= 25-11=14km/h

→ Distance=40km

→ Time=40/14= 2.85Hours

Difference between time

→ 2.85-1.6=1.25

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