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ICSE Class 10 Answered

find the sum of the first 24 terms of A.P., if it is known that - 1st term + 5th term + 10th term + 15th term + 20th term + 24th term =225
Asked by bdroy_2014 | 08 Feb, 2018, 01:37: PM
answered-by-expert Expert Answer

We have to find the sum of first 24 terms of an AP. 

S24 = 24/2 [ 2A + (24-1)D]

        = 24A + 276D

 

The sum of the first, 5th, 10th, 15th, 20th and 24th term = 225 

A + ( A + 4D) +( A + 9D) + ( A + 14D) + ( A + 19D) + ( A + 23D)= 225

; 6A + 69D= 225 - (1)

Multiply (1) by 6 and you get

24A + 276D = 1350. 

☺👍

 

 

 

Answered by | 08 Feb, 2018, 02:47: PM

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