Question

A car covers the first half of the distance between two places at 40 km/h and another half at 60 km/h. The average speed of the car is

• A. 40 km/h
• B. 48 km/h
• C. 50 km/h
• D. 60 km/h

Answer 1

Answer: (B)

48 km/h

Answer 2

Let's consider, $x =$ total distance covered by the car, Time taken to complete the half distance with velocity $v =40\, km / h$,
$t _{1}=\frac{ x }{2 \times 40}=\frac{ x }{80} hr \ldots . .(1)$
The time taken to complete another half distance with velocity $u =60 km / h$
$t _{2}=\frac{ x }{2 \times 60}=\frac{ x }{120} h$
The total time taken, $t = t _{1}+ t _{2}$
$t =\frac{ x }{80}+\frac{ x }{120}=\frac{ x }{48} h$
The average speed of the car,
$v_{\text{avg}} = \frac{x}{\frac{x}{48}} = 48 \text{ km/h}$