1.

A motorboat goes downstream in a river and covers a distance of 64km in 2 hours, while coming back to the starting point, the boat takes hours. The speed of the motorboat in still water and the speed of the stream respectively are :A. 20km/h and 8km/h B. 28km/h and 4km/hC. 30km/h and 2km/h D. 32km/h and 3km/h ​​

Answer»

Answer:

SPEED of boat = 30 km/h;

speed of stream = 2km/h;

Step-by-step EXPLANATION:

let stream speed be y and boat stream be X;

in general: S=D/T;

t=d/s(total);

s(total) (while  downstream)=x+y;

t(downstream) = d/(speed(downstream));

s(total) (while UPSTREAM)=x-y;

t(upstream) = d/(speed(upstream));

2= 64/(x+y);

2x +2y =64;........(1);

16/7=64/x-y;

16x-16y= 448;..............(2);

by multiplying (1 )*8

16x+16y=512;

16x-16y=448;

32x=960;

x=30;

2x+2y=64;(1)

60+2y=64;

2y=4;

y=2;

therefore, speed of boat = 30 km/h;

speed of stream = 2km/h;

hope you find this HELPFUL.


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