Latest Others Aptitude Question SOLUTION: Find the sum of first 24 terms of the A.P. a1, a2, a3, ... if it is known that a1 + a5 + a10 + a15 + a20 + a24 = 225

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(#M40007617) OTHERS question sum of series Keep an EYE

Find the sum of first 24 terms of the A.P. a1, a2, a3, ... if it is known that
a1 + a5 + a10 + a15 + a20 + a24 = 225

Asked In Others Sukham (12 years ago)

Solved Pargat Pal Singh Read Solution (3)

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Pargat Pal Singh  (12 years ago)

a1 + a5 + a10 + a15 + a20 + a24 = 225
(a1 + a24)+ (a5 + a20)+ (a10 + a15 ) = 225
but
(a1 + a24)= (a5 + a20)= (a10 + a15 )
hence
3*(a1+a24) =225
a1 + a24= 225/3 =75

sum of first 24 terms = (n/2)*(a+l) = 12*75 = 900

Is this solution Helpfull? Yes (8) | No   

Chetan Anand  (12 years ago)

We known that sum of 1st term and last term = sum of second term and second last term. Similarly, for all the numbers.
(a1+a24)+(a5+a20)+(a10+a15)=225
since, (a1+a24)=(a5+a20)=(a10+a15)
Therefore, (a1+a24) = 225/3 = 75
So for 2 terms sum = 75
Then for 24 terms = ((75*24)/2)=900

Is this solution Helpfull? Yes (3) | No   

Sukham  (12 years ago)

900 is correct.

Is this solution Helpfull? Yes | No (3)  

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