if a clock strikes once at 12 A.M. , twice at 1 A.M. , thrice at 2 A.M. and so on.How many times will the clock be struck in the course of 3 days? 1. 756. 2. 828. 3. 678. 4.1288

At 11pm 24 why 23

The answer is 900 the above solution has been copied from Arun sharma's answers which is wrong for this particular question

At 12AM Clock strikes once = 1
At 1AM Clock strikes twice= 2
At 2AM Clock strikes thrice=3
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At 11PM Clock strikes =23
After 3 days i.e. 72 hrs it'll strike 3(1+2+3+....+23) times.
So, the clock will strike= 3(1+2+3+....+23)
=n(n+1)/2
=3x24(23)/2
=23x12x3
=828

Sum of the series = n(n+1)/2
Series are as 1+2+3+....23 and here n= 23
So , putting value in the formula n(n+1)/2 , we get 23(24+1)/2 = 276
For 3 days, it will be 276 × 3 = 828 times.

At 11 pm clock strikes =24 times