Algebra college

Question

Pls help me..

A motorboat takes 4 hours to travel 192 kilometers up stream. The return trip takes 3 hours going to down stream. What is the the rate of the boat going up stream and what is the rate of the going down stream.

Answer 1

up stream speed is 192/4 = 48 km/hr

down stream speed is 192/3 = 64 km/hr

Usually this type of problem asks what is the speed of the stream and what is the speed of the motorboat in still water.

distance = speed times time, d=rt

let s= speed in still water, with r=rate of speed of the stream

192 =( s-r)4 = 4s-4r

192= (s+r)3= 3s+3r

multiply the 1st equation by 3 and the 2nd by 4 and subtract them

768 =12s+12r

576=12s-12r

192=24r

r = 192/24 = 32/4 = 8 km/hr = stream speed

3s=192-3(8) = 168

s = 168/3 = 56 km/hr

of course, you could have just averaged the two speeds, up and down stream (48+64)/2 =112/2 = 56 km/hr

for the speed in still water. then just subtract 56-48 = 8 km/hr for the stream speed