Question

A man travels a distance in three equal parts. he covers first part at 20kmph,second part at 40kmph and third part at 120kmph. find the distance if he covers total distance in 20hrs.

Answer 1

x1 = x2 = x3 = 1/3x total

t1 + t2 + t3 = 20 hours

x1 = v1 . t1
1/3x total = 20 . t1
x total = 60t1
t1 = 1/60x total

x2 = v2 . t2
1/3x total = 40 . t2
x total = 120t2
t2 = 1/120x total

x3 = v3 . t3
1/3x total = 120 . t3
x total = 360t3
t3 = 1/360x total

t1 + t2 + t3 = 20 
1/60x total + 1/120x total + 1/360x total = 20
6/360x total + 3/360x total + 1/360x total = 20
10/360x total = 20
1/36x total = 20
x total = 20 : 1/36
x total = 20 × 36/1
x total = 720 km