A man went 75 km in 7 hours . He went some distance at the rate of 12 km per hour and the rest at 10 km per hour. How far did he go at 12 km per hour?

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Solution

Total distance = 75 km
total time = 7hr
let suppose men went x km at rate of 12 km/hr.
then (75-x)km by 10km/hr.
(t1)time taken for 12km/hr=dist/speed
=x/12.
(t2)time taken for 10km/hr=dist/speed
=(75-x)/10
total time =(t1)+(t2)
7 =x/12+(75-x)/10
71210=10x+75*12-12x
840 = -2x+900
2x=60
x=30.
so, men went 30 km at rate of 12 km/hr.

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