A man started 20 min late and travelling at a speed of 11/2

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A man started 20 min late and travelling at a speed of 1¹/₂ times of his usual speed reaches his office in time. The time taken by the man to reach his office at his usual speed is ?

1. 40 min
2. 1 h 20 min
3. 1 h
4. 30 min

Correct Option: C

Let usual speed of a man is V and time is t h.
By the formula, V₁t₁ = V₂t₂
Vt = 1¹/₂ V(t - 20/60)
⇒ t = 3/2(t - 1/3)
⇒ 3/2 t - t = 1/2
∴ t = 1 h
Hence, the time taken by the man to reach his office at his usual speed is 1 h.