Question

A clock strike once at 1 o'clock twice at 2 o'clock and so on . How many times will it strikes after 24 hours

Answer 1

it will strike once at 1

twice at 2

and so on upto 12 times at 12

so the sum will be n(n+1)/2 = 12(13)/2 = 13*6 = 78 times in first 12 hours and 78 times in another 12 hours coz there are 24 hours in a day

so it will strike 156 times in 24 hours