# Aptitude - Compound Interest - Discussion

### Discussion :: Compound Interest - General Questions (Q.No.5)

5.

The compound interest on Rs. 30,000 at 7% per annum is Rs. 4347. The period (in years) is:

[A]. 2
[B].
 2 1 2
[C]. 3
[D]. 4

Explanation:

Amount = Rs. (30000 + 4347) = Rs. 34347.

Let the time be n years.

 Then, 30000 1 + 7 n = 34347 100  107 n = 34347 = 11449 = 107 2 100 30000 10000 100 n = 2 years.

 Chaitu said: (Nov 23, 2010) 30000(107/100)=32100 (32100*7)/100=147 is for 1 year 2100+2100+147=4347 2 years

 Dittya said: (Apr 5, 2011) Yaa, its because (107)^2 = 11449 and (100)^2 = 10000.

 Prabakaran said: (Jul 19, 2011) What is 107/100 ?

 Anusha said: (Oct 16, 2011) Amount=30000+4347 = 34347 amount=p(1+R/100)^n 34347=30000(1+7/100)^n 34347=30000(107/100)^n 34347/30000=(107/100)^n 11429/10000=(107/100)^n. hence (107/100)^2=11429/10000.

 Mercy said: (Jan 20, 2012) Simpler yet old-fashioned solution to me would be: 30000*7/100=2100 - year 1 30000+2100=32100*7/100=2247 - year 2 now add 2100+2247=4347 which was the compound interest earned after 2years. Thus the ans is 2 years.

 Swa1 said: (Aug 22, 2012) 4347=30,000(1+7/100)^n why not? and 30,000+4347=34,347 why? plz any one explian me.

 Usha said: (Sep 14, 2013) C.I will be the 4347. C.I = AMOUNT-PRINCIPAL. PRINCIPAL = 30,000. 4347 = AMOUNT-30000. AMOUNT = 4347+30000 = 34347. AMOUNT = P(1+R/100)^n. 34347 = 30000(1+7/100)^n. 34347/30000 = (107/100)^n.

 Sumit P. said: (Oct 25, 2013) Sorry Guys but it should; 11449 / 10000 // 34347 / 30000 is multiplied and divide by 3. Hence, Now 11449 and 10000 are squares of 107 and 100 resp. Thus(107 / 100)^ 2. Thus n = 2.

 Anshu said: (Dec 20, 2013) 30000*7/100 = 2100 - year 1. 30000+2100 = 32100*7/100 = 2247 - year 2. Now add 2100+2247 = 4347 which is 2 years.

 Hafsa Ali said: (Jan 2, 2014) Why we add 30,000 and 4347?

 Arpita Dey said: (Feb 26, 2014) How (107/100)^t = 34347/30000. t=2? I forgot the conversion.

 Manasa said: (Mar 7, 2014) What is the shortcut method for calculating the square root of 11449?

 Fizna said: (Nov 19, 2014) Can anyone say the exact formula for finding the period?

 Hitendra said: (Dec 2, 2014) How to calculate (107/100)^t = 34347/30000?

 Rajnish said: (Dec 11, 2014) Hi guys, I think (107/100)^t is not easy to find without using calculator. So, I want advice you play hit and trial. Take t = 1, t = 2, ..... and match your option.

 Tejas said: (Dec 15, 2014) Why 34347/30000?

 Digvijay said: (Dec 18, 2014) Ya! it's not easy to find out. We have to try with value of t.

 Isha Sharma said: (May 9, 2015) Guys this is simple divide numerator and denominator by 3 you will get your answer.

 Trilok said: (Sep 14, 2015) 11449/10000 = (107/100)^n , 1.1442 = (1.07)^n. We can write as log 1.1442 = n log 1.07, n = log 1.1442/log 1.07 = 0.058501/0.029383 = 2 (as per scientific calculator).

 Bhabani said: (Oct 20, 2015) A sum becomes double in ten years in C.I. So in how many years the principal would be 8 times?

 Leo said: (Nov 28, 2015) Can anyone explain me the simplification of (107/100)2?

 Abhilok said: (Dec 6, 2015) 2 times in 10 years. 2^3 = 8 times in 3*10 = 30 years. Let power = n. Given year = y. n*y is the answer.

 Dearlie Beloved said: (Dec 30, 2015) Shortcut through using ln: t = ln (34 347/30 000)/ln (1.07). t = 2 years.

 Anurag Nath said: (May 12, 2016) @Hitendra. (107/100)n = 11449/10000. => 107 * 107/100 * 100 = 11449/10000. => (107/100)2 = 11449/10000 [Here n = 2]. Therefore n=2.

 France said: (Jun 28, 2016) 107 * 107 is 11449 and 100 * 100 = 10000 but how is it equal to 34347/30000 ?

 Rkh said: (Nov 14, 2016) What if the power is( 107/100)^4?. How can we find quad root of a number?

 Chloe said: (Mar 27, 2017) Use the formula n = [ log(fv/p) ] / [ log (1+i)]. Where FV = future value. P = present value. i = interest ( in dec. place). n = [ log ( 34,347/30,000) ] / [ log (1+0.07)]. = 2.

 B. Tatung said: (May 9, 2017) How come 3 divided by both numerator and denominator? Please, someone, explain me.

 Akash Kumar Sinha said: (Jul 14, 2017) 1st year CI= 7% OF 30000 ie 2100. 2nd year CI=2100+ 7% of 2100 ie 147. 2100+2100+147=4347. Hence, 2 years.

 Priya said: (Jul 29, 2017) What is 107/100? I can't understand, please explain.

 Shipra said: (Aug 2, 2017) Thanks people. It helped a lot!

 Subramanyam said: (Aug 23, 2017) Thanks, friends. It helped a lot!

 Narsim Bari said: (Feb 27, 2018) 30000*7/100 = 2100 for 1rst year. For 2nd year : 30000+2100*7/100 = 2247. Now, cross-check the given calculated amount given in the question itself i.e 4347 rupees by adding 2 years amount (2100+2247)=4347. Believe this is the fastest and tricky method of our natural mind.

 Prasad said: (Jun 15, 2018) Why we square that 107/100 n=2? why? please.

 Sangavi said: (Dec 9, 2018) Why we add 30000 and 4347, can anyone please explain it?

 Bimla Jarmwal said: (Jan 4, 2019) Please, anyone, explain the answer in detail to me.

 Anomie said: (Jan 29, 2019) How did come 11449?

 Lokesh said: (Mar 21, 2019) Verify with given option. CI =7 % 1ST YEAR 7%. For 2nd year, it becomes 7.49 Total 14.49 If 100% = 30K. Then 114.49 = ? (114.49 * 30K)÷100. And you will get 4347.

 Migma Tshering Tamang said: (Oct 12, 2020) 34347=30000(1+0.07)^n. 1.1449=(1.07)^n. Using log in both the side. log1.1449=n * log1.07. n=log1.1449/log1.07. n=2 years.

 Saron said: (Oct 25, 2021) Very good, Thanks everyone for explaining.

 Garima said: (Dec 9, 2021) Can anyone please tell me how (1+7/100) become (107+100)?

 Nitish said: (May 2, 2022) No @Garima. You should write it as 107/100 which came by the basic addition method.