A man started 10 minutes late from his home to his office. He travelled at a speed of  times of his usual speed and reached his office in time. Then the time taken by the man to reach his office at his usual speed is (in minutes)  

 

Given:

The man started 10 minutes late, traveled at (i.e 5/4) times his usual speed, and reached his office in time.

Formula used:

Time = Distance / Speed

Calculation:

Let the usual time taken to reach the office be T minutes.

At 5/4 times the speed, the new time taken = T × (4/5).

Since he reached on time despite being 10 minutes late:

T × (4/5) + 10 = T

⇒ T × (4/5) + 10 = T

⇒ T - 4T/5 = 10

⇒ T/5 = 10

⇒ T = 50

∴ The correct answer is option (1).