Question

a certain sum of money doubles itself in ten years .. what would be the amount of time it would triple itself and triple again. IT'S A CHALLENGE FOR EVERY MATHS GENIUS

Answer 1

Solution:-
Let the Principal be Rs. 100.
According to the question.
Rs. 100 doubles itself in 10 years.
Simple interest = P*R*T/100 + 100 = 200
= 100*R*10/100 = 200 - 100
= 10R = 100
Rate of interest = 10 %
Therefore, Rs. 100 ÷ 10 years = Rs. 10 increase per year.
 Money tripled = 100*3 = Rs.300
There is a increase of Rs. 10 per year
So, Rs. 200 increase in = 200/10
= 20 years.
The money will triple in 20 years.
Then triple again in how many years.
After 20 years the Principle becomes Rs. 300 (Principle Rs. 100 + Interest Rs. 200 for 20 years)
Now, its triple means 300*3 = Rs. 900
So, Rs. 900 - Rs. 300 = Rs. 600 (Interest)
If Rs. 10 increases in 1 year
Then Rs. 600 will increase in years = 600/10 
= 60 years.
So, the money will triple again in 60 years.
Answer.