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प्रश्न
A man saved Rs 66000 in 20 years. In each succeeding year after the first year he saved Rs 200 more than what he saved in the previous year. How much did he save in the first year?
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उत्तर
Let Rs. x be saved in first year
Annual increment = Rs. 200
Which forms an A.P.
First term = a and common difference d = 200
n = 20 years
∴ Sn = `n/2[2a + (n - 1)d]`
⇒ S20 = `20/2 [2a + (20 - 1) 200]`
⇒ 66000 = 10[2a + 3800]
⇒ 6600 = 2a + 3800
⇒ 2a = 6600 – 3800
⇒ 2a = 2800
⇒ a = 1400
Hence, the man saved Rs. 1400 in the first year.
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