Compound Interest
- The difference between the compound interest and the simple interest on a certain sum at 5% per annum for 2 years is Rs. 1.50. The sum is ?
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Let the sum be Rs. 100 then,
S.I.= Rs.(100 x 5 x 2)/100 =Rs.10
C.l.= Rs.[100 x (1 +5/100)2] =Rs.41/4
∴ difference between C.I. and S.I. = Rs. (41/4-10) = Re.0.25Correct Option: A
Let the sum be Rs. 100 then,
S.I.= Rs.(100 x 5 x 2)/100 =Rs.10
C.l.= Rs.[100 x (1 +5/100)2] =Rs.41/4
∴ difference between C.I. and S.I. = Rs. (41/4-10) = Re.0.25
⇒ 0.25 : 1.50 : : 100 : P
∴ P = (1.50 x 100) / 0.25 = Rs. 600
- The simple interest on a certain sum for 2 years at 10% per annum is Rs.90. The corresponding compound interest is?
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Principle = (100 x interest) / (time x rate)
⇒ Sum = (100 x 90) / (2 x 10) = Rs. 450Correct Option: C
Principle = (100 x interest) / (time x rate)
⇒ Sum = (100 x 90) / (2 x 10) = Rs. 450
C.I. =Rs.[ 450 x (1 + 10/100)2 - 450] = Rs. 94.50
- What is the principle amount which earns Rs. 132 as compound interest for the second years at 10% per annum ?
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Let P the principle at the end of first year.
Then (P x 10 x 1)/100 =132
⇒ P =1320
Let Q be the original principle
Then, Q + (Q x 10 x 1)/100 =1320
⇒ Q =1200Correct Option: B
Let P the principle at the end of first year.
Then (P x 10 x 1)/100 =132
⇒ P =1320
Let Q be the original principle
Then, Q + (Q x 10 x 1)/100 =1320
⇒ Q =1200
- Simple interest on a sum at 4% per annum for 2 years is Rs.80. The compound interest on the same sum for the same period is ?
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principle = (interest x 100) / (time x rate)
= Rs. (100 x 80)/(4 x 2) = Rs. 1000
∴ C.I. =Rs.[{1000 x (1 + 4/100)2 - 1000}]
Correct Option: A
principle = (interest x 100) / (time x rate)
= Rs. (100 x 80)/(4 x 2) = Rs. 1000
∴ C.I. =Rs.[{1000 x (1 + 4/100)2 - 1000}]
= Rs. 81.60
- The least number of complete years in which a sum of money put out at 20% compound interest will be more than doubled is ?
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∵ P x (1 + 20/100)t > 2P
⇒ (6/5)n > 2Correct Option: B
∵ P x (1 + 20/100)t > 2P
⇒ (6/5)n > 2
Now, (6/5) x (6/5) x (6/5) x (6/5) > 2
⇒ 1296/615 > 2
∴ t = 4 years