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The simple interest on a certain sum for 8 years at 12 per cent per annum is ₹ 3120 more than the simple interest on the same sum for 5 years at 14 per cent per annum. Find the sum. - Mathematics

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Question

The simple interest on a certain sum for 8 years at 12 per cent per annum is ₹ 3120 more than the simple interest on the same sum for 5 years at 14 per cent per annum. Find the sum.

Sum

Solution

Given, I1 – I2 = ₹ 3120

T1 = 8 yr, R1 = 12%

T2 = 5 yr, R2 = 14%

And P1 = P2 = P

According to the question,

I1 – I2 = ₹ 3120

⇒ `(P_1 xx R_1 xx T_1)/100 - (P_2 xx R_2 xx T_2)/100` = 3120

⇒ `(P xx 12 xx 8)/100 - (P xx 14 xx 5)/100` = 3120

⇒ `P/100 [12 xx 8 - 14 xx 5]` = 3120

⇒ P[96 – 70] = 3120 × 100

⇒ 26P = 312000

⇒ P = `312000/26`

∴ P = ₹ 12000

Hence, the sum is ₹ 12000.

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Chapter 7: Comparing Quantities - Exercise [Page 214]

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NCERT Exemplar Mathematics [English] Class 7
Chapter 7 Comparing Quantities
Exercise | Q 134. | Page 214

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