simple interest

[naaga]

The simple interest in a sum of money will be Rs. 600 after 10 years. If the principal is trebled after 5 years, what will be the total interest at the end of the 10th year ?

800

900

1200

1500

1800

OA is C

[DanaJ]

The trick is with the simple interest here: say you have a rate of x simple interest, which means that in one year you will have x*S (with S = sum of money invested) interest to collect. Since it is a simple interest, it isn't capitalized, so in 10 years you basically get 10 times x*S or 10xS.
We are told that this 10xS = 600.
Now, in 5 years you will get 5*xS interest. After 5 years, S will be tripled, making the interest you get per one year x*(3S) or 3xS. For the remaining 5 years you will get 5 * 3xS = 15xS.
Now let's see the total interest:
interest for the first 5 years: 5xS.
interest for the last 5 years: 15xS.
Add them up to get 20xs or 2*(10xS). Since we know that 10xs = 600, the solution to the problem will be 1200 or 2*600.

[NareshCS]

say the principle as x

the principle gives 600 as interest in 10 years. implies it gives 300 interest in 5 years

after 5 years the principle is tripled. the interest for remaining 5 years is also 3 times 300= 900

total interest we get at the end of 10 years= 900+300= 1200

[Shubhi gupta]

The simple interest in a sum of money will be Rs. 600 after 10 years. If the principal is trebled after 5 years, what will be the total interest at the end of the 10th year ?

800

900

1200

1500

1800

OA is C