Question

A motorboat, whose speed in 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km/hr) is:

Answer 1

Speed =15;d=30;let spred of stream be x. Downstream. time= 30/(15+x).....Upstream, time =30/(15-x)......Total time =4 1/2 =9/2 hr. Therefore,30{1/(15+x)+1/(15-x)}=9/2......10{(15+x+15-x)/(225-x^2)}=3/2......300/(225-x^2)=3/2....100/(225-x^2)=1/2....200= 225-x^2...x^2=225-200....x^2=25....x=5 km/hr