Question

SURESH STARTED HIS JOURNEY FROM P TO Q BY HIS BIKE AT THE SPEED OD 40 KM/HR AND THEN , THE SAME DISTANCE HE TRAVELLED ON HIS FOOT AT THE SPEED OF 10 KM /HR FROM Q TO R. THEN HE RETURNED FROM R TO P VIA Q AT THE SPEED OF 24 KM/ HR ..the average spped of the whole is.
A)18.5KM/HR
B) 19.8
C) 18.2
D)19.2

Answer 1

Solution :-

Let the distance from P to Q be 'x' km and Q to R be 'x' km (as the distance from P to Q and from Q to R is same).

So, the distance from R to P via Q will be 2x.

Time taken from P to Q (t1) = x/40 hr
Time taken from Q to R (t2) = x/10 hr
Time taken from R to P via Q (t3) = 2x/24 hr

Total distance = 4x km

Total time taken = x/40 + x/10 + 2x/24

Taking LCM of the denominators and then solving it.

⇒ (3x + 12x + 10x)120

⇒ 25x/120

So, total time taken is 5x/24 hrs

Speed = Distance/Time

⇒ 4x ÷ 5x/24

⇒ 4x*24/5x

⇒ 96x/5x

⇒ 96/5

⇒ 19.2 km/hr

So, average is 19.2 km/hr

Option (D) is correct.