Shaun invests a certain sum of money at 18.75% p.a. simple interest.

Question

Shaun invests a certain sum of money at 18.75% p.a. simple interest. After how many years will the sum of money become three times its principal?

A. 10 years, 6 months, 20 days
B. 10 years 8 months
C. 10 years 9 months
D. 12 years
E. 16 years

D3N0 · Accepted Answer

Ans: B
Solution: simple interest question

B=A ; where A is principal amount, B final amount, t time in years and r interest rate
after putting the values 18.75= 75/4

3=  
t= 32/3 which is (30+2)/3= 10 + 2/3 means 10 years and (12*2)/3 = 8 months.
total time 10 years 8 months

AnkitaAnkita · Answer

ANS IS E

P= PRINCIPAL AMOUNT
T = YEARS/MONTHS 
S.I =

P * 18.75 * T / 100 = 3*P

SOLVING FURTHER

T = 100 * 100 / 625

T=16 YEARS

AnkitaAnkita · Answer

You have wrongly used CI formula for SI.

D3N0 · Answer

you used formula for interest only : 
question is asking about total sum of money.
 so formula is

Final sum = Initial amount

AnkitaAnkita · Answer

Yep sorry!

Lesson learnt
Read properly

D3N0 · Answer

Yes and one more thing the interest formula you used is also wrong as in you shouldn't use it this way because it makes you prone to making mistakes. just use Interest = (amount* rate)/100 and you multiply with time in later part so that you don't get confused and use it wrongly. just an advice. Thumbs UP :-D

AnkitaAnkita · Answer

Sure thing. I did not understand how i can use it wrongly. But will be cautious . Thanks.

P.S: The formula is right but the steps followed may take me down. And just to tell you: When you are an engineer ,you don't focus on the formulas , just use it like a key to the answer choice. You become quick in putting everything together . perhaps , that is the bad habit.

D3N0 · Answer

Unfortunately or Fortunately I am an engineer too. I used to do the same mistake but now I take my time because 10 seconds can make difference.

AnkitaAnkita · Answer

Now i am going to follow you!
Thankyou

jimmy02 · Answer

Total Amount=Prnciple+SI
3P=P+PxRxt
3P=P(1+18.75%t)
t=32/3
t=10 years 8 months

Ans is 'B'

Jimmy

mathivanan · Answer

Let 100 be the principal
You have to earn 200 as interest
Divide 200 by 18.75 to get the number of years (10 and 2/3; 2/3 is 8 months)
It is 10 years and 8 months.

lenric · Answer

Basically, the sum of the money gathered with the interest must be 200 usd.

If we consider the principal to be 100 usd, we'll quickly realize that options D and C are wrong. 
Now in one year we'll get an interest of 100 * 0,1875 = 18,75. In 10 years we'll have 187.5 Obviously, in 11 years we'll have more than 200 usd, thus the previous paragraph.

We need 12,5 usd. Now, if we're used to do mental calculation, we'll quickly realize that 18/3 + 0,75/3 = 6 + 0,25 = 6,25. And 6,25*2 = 12,5 -> 2/3 of 18,75, which is what we get in 1 year, hence we'll need 2/3 of a year, which is answer b) -> 8 months.

HoudaSR · Answer

P+(Px18,75%xT)=3P
Px18,75%xT=2P
18,75%xT=2
T=2x100/18,75

Can anyone tell me how to calculate this without a calculator?

rahumangal · Answer

In S.I, rates simply multiply with the principal amount so, we only need to check when the rate becomes 200% for the whole amoount to become 300% or 3 x principal amount

so, 18.75% x time = 200%
 75/4 x time = 200
 time = 10+2/3 years
 = 10 yrs+ 8 months

Kinshook · Answer

Given: Shaun invests a certain sum of money at 18.75% p.a. simple interest. 
Asked: After how many years will the sum of money become three times its principal?

Simple interest = Principal * Rate * Time = x * .1875 * t = 2x
t = 2/.1875 = 10.66 years = 10 years 8 months

IMO B

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Shaun invests a certain sum of money at 18.75% p.a. simple interest.

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