Question

A boat can cover 7.8 km upstream in 18 min .if the speed of the stream is 3.5 kmph , how much distance can the boat cover downstream in 26 minues?

Answer 1

Solution:-
Here,
Speed of upstream is 3.5 KMPH
Distance in Upstream = 7.8 KM
Time taken in Upstream = 18 minutes = 0.3 Hour

So, Here We have to find out speed of boat in still water.
Let the speed of boat in still water be x - 3.5 KMPH
so,
time = distance/speed
0.3 KM = 7.8 KM/x - 3.5 KMPH
3( x - 3.5)= 7.8 * 10
3(x - 3.5) = 78
x - 3.5 = 78/3
x - 3.5 = 26
x = 26 + 3.5
x = 29.5
So, the speed of boat in still water is 29.5 KMPH.
Now,
time taken to boat in downstream = 26 minutes = 13/30 He
speed of boat in downstream = (speed of boat in still water) + (Speed of Stream)
speed of boat in downstream = (29.5 + 3.5)KMPH
= 33 KMPH
Now,
Distance covered in downstream = Speed × Time
Distance covered in downstream = 33 × 13/30
= 13 × 11/10
= 14.3 KM

Hence, the boat can covered a distance of 14.3 kilometres in downstream in just 26 minutes.
[Please Kindly prefer to NCERT mathematics class 10 Chapter 4 Quadratic Equations Page 87 Example 15. This question is based on example 15]