<PRE><B>Question 792848</B>
A boy can swim down stream four times as fast as he swim up stream.
 If he can swim up stream and down stream in a total of 22 minutes, how many minutes does it takes him to swim upstream.
:
let the one-way distance = 120 m
let s = his speed up stream
then
4s = his speed downstream
;
Write a time equation time = dist/speed
:
Upstr time + downstr time = 22 min
{{{120/s}}} + {{{120/(4s)}}} = 22
Multiply eq by 4s to clear the denominators
4(120) + 120 = 4s(22)
480 + 120 = 88s
s = 600/88
s = 6.82 m/min his upstream speed
find the time upstream
120/6.82 = 17.6 min to swim upstream
:
Check this by finding the time down stream
120/(4*6.82) = 4.4 min
Total time 4.4 + 17.6 = 22 min</PRE>