A sum of Rs 15 600 is invested partly at 7 per annum and the remaining at 9 per annum simple interes...........

Quantitative Aptitude (CPO) Simple Interest

A sum of Rs 15,600 is invested partly at 7% per annum and the remaining at 9% per annum simple interest. If the total interest at the

end of 3 years is Rs 3,738. how much money was invested at 7% per annum?

This questions was previously asked in

SSC CPO 13th-March-2019-Shift-1

Rs 7,800

Rs 7,900

Rs 7,600

Rs 7,700

Let's break it down:

- Rs 15,600 is split into two parts: one at 7%, one at 9%, both for 3 years.

- Total interest after 3 years is Rs 3,738.

Let the amount at 7% = x

So, amount at 9% = 15,600 – x

Interest for each part:

- At 7%: x × 7 × 3 / 100 = 0.21x

- At 9%: (15,600 – x) × 9 × 3 / 100 = 0.27(15,600 – x)

The total interest: 0.21x + 0.27(15,600 – x) = 3,738

0.21x + 4,212 – 0.27x = 3,738

0.21x – 0.27x = 3,738 – 4,212

–0.06x = –474

x = 7,900

Option 2: Rs 7,900 is correct—this is the amount invested at 7% per annum.

- Option 1 (Rs 7,800), Option 3 (Rs 7,600), Option 4 (Rs 7,700) aren’t correct—they don’t satisfy the interest equation.

- What this really means is, you split your principal so the interest totals work out, and Rs 7,900 is the right way to go.

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