If new speed is a⁄b of original speed, then usual time × (b⁄a - 1) = change in time
∴ usual time × (4⁄3 - 1) = 1⁄3
⇒ usual time = 1⁄3 × 3 = 1 hr
If a man walks to his office at 3/4 of his usual rate, he reaches office 1/3 of an hour later than usual. What is his usual time to reach office.

[1] 1⁄2 hr
[2] 1 hr
[3] 3⁄4 hr
[4] 2 hrs
[5] None of these