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The difference between C.I. and S.I. on Rs. 7,500 for two years is Rs. 12 at the same rate of interest per annum. Find the rate of interest. - Mathematics

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Question

The difference between C.I. and S.I. on Rs. 7,500 for two years is Rs. 12 at the same rate of interest per annum. Find the rate of interest.,

Sum
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Solution

Given: P = Rs. 7,500 and Time (n) = 2 years

Let rate of interest = y%

∴ S.I. = `[ "P" xx "R" xx "T" ]/100` 

= `[7500 xx y xx 2]/100` 

= Rs. 150y

∴ C.I. = P`(1 + r/100)^n - "P"` 

= `"Rs". 7,500( 1 + y/100 )^2 - "Rs."  7,500`

Given: C.I. : S.I. = Rs. 12

⇒ `7,500[ 1 + y/100 ]^2 - 7,500 - 150y = 12`

⇒ `7,500[ 1 + y^2/10000 + (2y)/100 ] - 7,500 - 150y = 12`

⇒ `7,500 + [7500y^2]/[10000] + 150y - 7,500 - 150y = 12`

⇒ `(3y^2)/4 = 12`

⇒ y2 = 16          

⇒ y = 4%

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Concept of Compound Interest - When the Time is Not an Exact Number of Years and the Interest is Compounded Yearly
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Chapter 3: Compound Interest (Using Formula) - Exercise 3 (D) [Page 53]

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Selina Concise Mathematics [English] Class 9 ICSE
Chapter 3 Compound Interest (Using Formula)
Exercise 3 (D) | Q 6 | Page 53
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