Question
Sum of first 25 terms in AP is 525, sum of the next 25 terms is 725, what is the common difference?
- 8/25
- 4/25
- 6/25
- 1/5
Correct Answer : 8/25. Correct Choice : (1)
Explanatory Answer
The sum of the first 25 terms, S
25 = 525
The sum of the next 25 terms, K
25 = sum of next 25 terms = 725
a
26 = a
1 + 25d
a
27 = a
2 + 25d
K
25 = a
26 + a
27 + ...... + a
50
Or K
25 = a
1 + 25d + a
2 + 25d + ...... + a
25+ 25d
Or K
25 = a
1 + a
2 + ...... + a
25+ 25(25d)
Or K
25 = S
25 + 25(25d)
i.e., 725 = 525 + 25 x 25d
200 = 25 x 25d
8 = 25d
d = 8/25
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