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July 18th, 2019, 08:18 AM  #1 
Senior Member Joined: Aug 2014 From: India Posts: 470 Thanks: 1  Just answer this doubts from S.I problem.
If a sum of money amounts to Rs 12900 and Rs 14250 at the end of 4th and 5th year respectively at a certain rate of S.I , then the rate of interest is: 4 yrs  12900 5 yrs  14250 → 1 yrs  1350. → 1350 * 4 = 5400. 12900  5400 = 7500 R = (1350/7500) * 100 = 18% I didn't understand why 1350 is multiplied with 4? why 5400 is subtracted from 12900? 
July 18th, 2019, 11:53 PM  #2 
Senior Member Joined: Apr 2014 From: UK Posts: 963 Thanks: 342 
Each year you gain 1350, so after 4 years you have gained 5400. Since we want to know the initial amount so that we can work out the interest rate, we need to subtract the interest for 4 years (5400) from the 'after 4 years' value of 12900.


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