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A borrowed ₹ 4800 from B at 9% per annum simple interest for 3 yr. He, then added some more money to the borrowed sum and lent it to C for the same period at 12% per annum simple interest. If A gains ₹ 720 in the whole transaction, how much money did he add from his side ?
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- ₹ 500
- ₹ 740
- ₹ 640
- ₹ 800
Correct Option: D
Let the money added be ₹ P, Then,
[(4800 + P) x 12 x 3]/100 - (4800 x 9 x 3)/100 = 720
⇒ (4800 + P) x 36 - (4800 x 27) = 720 x 100
⇒ (4800 + P) x 4 - (4800 x 3) = 8000
⇒ 4800 + P - (1200 x 3 ) = 2000
⇒ P + 1200 = 2000
∴ P = 800
So, money added is ₹ 800.
