find the sum of number between 90 and 180 which are divisible by 7
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Answer:
91,117,150,144,156,121,120,130,
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To Find :- find the sum of number between 90 and 180 which are divisible by 7 ?
Answer :-
- First number between 90 and 180 which is divisible by 7 = a = 91 .
- Last number = T(n) = 175 .
- common difference = d = 7 .
so,
→ T(n) = a + (n - 1)d
→ 175 = 91 + (n - 1)7
→ 175 = 91 + 7n - 7
→ 175 = 84 + 7n
→ 175 - 84 = 7n
→ 7n = 91
→ n = 13 .
then,
→ S(n) = (n/2)[2a + (n - 1)d]
→ S(n) = (13/2)[2*91 + 12*7]
→ S(n) = (13/2)[182 + 84]
→ S(n) = (13/2) * 266
→ S(n) = 1729 (Ans.)
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