Aptitude - Compound Interest - Discussion
Discussion Forum : Compound Interest - General Questions (Q.No. 15)
15.
The compound interest on a certain sum for 2 years at 10% per annum is Rs. 525. The simple interest on the same sum for double the time at half the rate percent per annum is:
Answer: Option
Explanation:
Let the sum be Rs. P.
| Then, |  |
P |  |
1 + | 10 |  |
2 | - P |  |
= 525 |
| 100 |
 |
P | |
|
11 | |
2 | - 1 | |
= 525 |
| 10 |
| P = |
|
525 x 100 | |
= 2500. |
| 21 |
Sum = Rs . 2500.
| So, S.I. = Rs. | |
2500 x 5 x 4 | |
= Rs. 500 |
| 100 |
Discussion:
37 comments Page 2 of 4.
P Kumar said:
1 decade ago
CI = Amount - Principle.
525 = Principle(1+10/100)^2 - Principle.
Rate = 10, Time = 2.
525 = Principle(110/100)^2 - Principle.
525 = Principle((22/20)^2-1)).
525 = Principle(121/100-1).
525 = Principle (21/100).
Principle = (525*100)/21.
Principle = 2500.
Now to calculate S.I principle = 2500 T=4 (double the time taken for C.I i.e 2*2 = 4).
R = 5 (Half of the rate taken for C.I i.e 10/2 = 5).
S.I = (P*T*R)/100.
S.I = (2500*4*5)/100.
S.I = 500.
525 = Principle(1+10/100)^2 - Principle.
Rate = 10, Time = 2.
525 = Principle(110/100)^2 - Principle.
525 = Principle((22/20)^2-1)).
525 = Principle(121/100-1).
525 = Principle (21/100).
Principle = (525*100)/21.
Principle = 2500.
Now to calculate S.I principle = 2500 T=4 (double the time taken for C.I i.e 2*2 = 4).
R = 5 (Half of the rate taken for C.I i.e 10/2 = 5).
S.I = (P*T*R)/100.
S.I = (2500*4*5)/100.
S.I = 500.
(1)
Mounika said:
9 years ago
Is there any shortcut way to solve this problem? If yes means please share.
Kiran said:
9 years ago
Can anyone tell the simple form to get the value of p?
Tshering choden said:
9 years ago
Why did we subtract -1 in place of - p? I can't get this step, help me.
Chetana said:
9 years ago
Because they took p to be common @Tshering.
R.b said:
9 years ago
Thank you, P.Kumar. Very well explained.
Sanjeev Sharma said:
9 years ago
We can always take base as 100.
On 100 CI for 2 yrs @10% = 21,
Now since CI is 525, therefore, P = 100 ÷ 21 * 525 = 2500,
Now SI = 2500 * 10 * 2 ÷ 100 = 500.
On 100 CI for 2 yrs @10% = 21,
Now since CI is 525, therefore, P = 100 ÷ 21 * 525 = 2500,
Now SI = 2500 * 10 * 2 ÷ 100 = 500.
Tina said:
9 years ago
Can anyone explain how -1 at place P?
Raghav said:
9 years ago
It's very simple just look at the question you have a direct relation between amount 525 and 10%.
For 2 years u get 525 at 10% for 1 year it is around 260. So if u invest around 2500 for 1 year at 10% the amount u get as interest is 250 but compound interest is slightly higher than simple interest and remember this is logical.
Now just put sum in simple interest formula
2500 * 4 * 5/100 = 500.
For 2 years u get 525 at 10% for 1 year it is around 260. So if u invest around 2500 for 1 year at 10% the amount u get as interest is 250 but compound interest is slightly higher than simple interest and remember this is logical.
Now just put sum in simple interest formula
2500 * 4 * 5/100 = 500.
Kapricious said:
9 years ago
As they are saying 10% per annum and 2 years in time, we can be sure that Rs 21 gained as interest for Rs 100 in 2 years.
So, C.I is 21 when Principal is 100.
if C.I equal 525, the principal will be (100 * 525)/21.
= 2500.
So, C.I is 21 when Principal is 100.
if C.I equal 525, the principal will be (100 * 525)/21.
= 2500.
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