Amit saves $ 400 in the first month$ 500 in the second month in the third month$ 600 and so on .
How much will be his total savings in 21 months?
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Answer:
(A.P) = 400, 500, 600....
Term 1 = a = 400
d = 500 400 = 100
n = 21
So,
tn = a + (n-1) × d
= 400+ (211) × 100
= 400 + 20 × 100
= 400 + 2000
tn= 2400
Sn = n/2 (term 1 + tn)
= 21/2 (400 + 2400)
= 21/2 (2800)
= 21 x 1400
= 29400
So his total savings will be 29400 rs
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