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प्रश्न
A man accepts a position with an initial salary of Rs 5200 per month. It is understood that he will receive an automatic increase of Rs 320 in the very next month and each month thereafter. What is his total earnings during the first year?
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उत्तर
Given that fixed increment in the salary of a man
= Rs. 320 each month
Initial salary = Rs. 5200 which makes an A.P.
whose first term (a) = Rs. 5200 and common difference (d) = Rs. 320
Total earning during the first year (12 months)
S12 = `12/2 [2 xx 5200 + (12 - 1) xx 320]` .....`[because "S"_n = n/2 [2a + (n - 1)"d"]]`
= 6[10400 + 3520]
= 6 × 13920
= Rs. 83520
Hence, the required amount is Rs. 83520
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