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प्रश्न
A man saved ₹ 16500 in ten years. In each year after the first, he saved ₹ 100 more than he did in the preceding year. How much did he save in the first year?
उत्तर
S10 = ₹ 16500
a, a + d, a + 2d ...
d = 100
n = 10
Sn = `"n"/2` (2a + (n – 1)d)
S10 = 16500
S10 = `10/2` (2 × a + 9 × 100)
16500 = 5(2a + 900)
16500 = 10a + 4500
10a = 16500 – 4500
10a = 12000
a = `12000/10` = ₹ 1200
∴ He saved ₹ 1200 in the first year
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