Question

At a certain rate of simple interest, a certain sum doubles itself in 10 years. In how many years will it triple itself?

Answer 1

15 years?

Answer 2

How??

Answer 3

I think your answer is correct lgbasallote, because 15 is one of the options.

Answer 4

what i did was it doubles in 10 years...so it quadruples in 20...in between is 150 -> triple

Answer 5

15*

Answer 6

I there no other way?

Answer 7

*Is

Answer 8

i dont know...seems there is an algebraic equation for it..but i cant equate it..

Answer 9

Can we take the rate as a constant(say, 5%) and the principal as x?

Answer 10

ratio and proportion can be used too i guess

2:10 = 3:x

30 = 2x

x = 15

Answer 11

@amistre64 can you help?

Answer 12

ln(2) = 10 ln(1+ r/100) => rate must be 7.17735

ln(3) = x ln(1+ 7.17735/100) => x = 15.8496
http://www.wolframalpha.com/input/?i=solve+ln%283%29+%3D+x+ln%281%2B+7.17735%2F100%29

Answer 13

But its not compound interest, its simple interest.

Answer 14

What is In?

Answer 15

I = PTR/100 => I = P => R => 100/10

for tripling

2I = PTR/100 => T=15

Answer 16

How is I = P(in the second step)??

Answer 17

for sum to double .. . you need Interest = Principal => I+P = A = 2P
and same logic goes for tripling

Answer 18

Oh, I see... thanks.

Answer 19

Sorry to trouble you but how is R = 100/10.

Answer 20

@experimentX

Answer 21

I and R cancel out
I = PTR/100 =>1 = TR/100 => T = 10 => 1 = R10/100 => R = 100/10

Answer 22

Thanks.