Correct Answer - Option 1 : 60, 80
Given:
If the speed of car B is decreased by 10 kms per hour, the average speed of car B and C will be 70 km/hr. If the speed of car A is increased by 10 km/hr, the average speed of cars A and C will be 70 km/hr. The average speed of cars A and B is 70 km/hr.
Formula:
Average of n numbers a1, a2 ... an = (a1 + a2 + ... an)/n
Calculation:
Let the speed of car B be b and speed of car A be a and C be c respectively.
New speed of card B = b – 10
Given,
(b – 10 + c)/2 = 70
b + c = 150 ----(1)
New speed of car A = a + 10
Given,
(a + 10 + c)/2 = 70
a + c = 130 ----(2)
Average speed of cars A and B is 70 km/hr
(a + b)/2 = 70
a + b = 140 ----3
Adding (2) and (3)
2a + b + c = 270
2a + 150 = 270
2a = 120
a = 60
b = 80
c = 70