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12. Kavita has a cumulative time deposit account in a bank. She deposits 800 per month andgets 6700 as maturity value. If the rate of interest be 5% per annum, find the total timefor which the account was held.[Hint: x2 + 481x-10020-0 x2 + 501x-20x-10020 = 0.1 |
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Answer» Let time be x monthsQualifying amount= 800x(x+1)/2 = 400x(x+1) SI = 400x(x+1)*5*1/1200 = (1/3)x(x+1)*5 = (5/3)x(x+1)Principal = 800x Hence,800x + (5/3)x(x+1) = 167002400x + 5x^2 + 5x = 16700*3x^2 + 481x - 10020 = 0x^2 + 501x - 20x - 10020 = 0x(x + 501) - 20(x + 501)(x - 20)(x + 501)x = 20, - 501 Negative value not possible Therefore, time for which account is held = 20 months |
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