Using AP find sum of all 3 digit no. Divisible by 7
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3 Digit Numbers divisible by 7 are as follows: 105, 112, ......, 994
a = 105
an = 994
d = 112 - 105 = 7
an = a + (n - 1)d
994 = 105 + (n - 1)7
(n - 1)7 = 994 - 105
(n - 1)7 = 889
n - 1 = 889/7
n - 1 = 127
n = 128
Sn = (n/2)*(a + an)
S128 = (128/2)*(105 + 994)
S128 = (64)*(1099)
S128 = 70336 ——> Answer
a = 105
an = 994
d = 112 - 105 = 7
an = a + (n - 1)d
994 = 105 + (n - 1)7
(n - 1)7 = 994 - 105
(n - 1)7 = 889
n - 1 = 889/7
n - 1 = 127
n = 128
Sn = (n/2)*(a + an)
S128 = (128/2)*(105 + 994)
S128 = (64)*(1099)
S128 = 70336 ——> Answer
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