Question

A certain police vehicle is on patrolling for road safety. Patrolling starts sharply at $6^{\prime }o$ clock and the vehicle comes again on the same road after $20$ minutes. Then at what time the vehicle come again on the same road for the $10th$ time.

• A. $7^{\prime }o$ clock
• B. $8^{\prime }o$ clock
• C. $9^{\prime }o$ clock
• D. ${10}^{\prime }o$ clock

Answer 1

The correct option is C $9^{\prime }o$ clock

We have to find the total time after the vehicle comes again
This forms an arithmetic sequence with first term $0$ and common difference $20$
$0,20,40,60,......$
$a_n=a+(n-1)d{a}_{10}=0+(10-1)20a_{10}=180$
So the vehicle will come for the tenth time after $180$ minutes
$180$ minutes $=$ $3$ hours
So the vehicle will come for the tenth time at $9^{\prime }o$ clock