Find the sum: 25 + 28 +31 +........... + 100.
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Answer:
a = 25
d = 3
l = 100
l = a + (n - 1) d
100 = 25 + (n - 1)3
75 = 3n - 3
3n = 78
n = 78/3 = 26
Now
Total sum = n/2( a + l )
= 26/2 ( 25 + 100)
= 13 × 125
= 1625 Ans...
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