Question

a certain sum of money at a certain rate of simple interest doubles it self in 10 years in how many years will the same sum become three times at the same rate of interest

Answer 1

let the sum be rs x
t=10yrs
amount =2x
si=a-p
=2x-x
=x

rate= x/x*100/10
=10%

sum is x
amount =3x
si=3x-x
=2x
time=2x/x*100/10
=20years

Answer 2

hi friend!!

here is your Answer!!
_________________________________

Let the principle be 100.

Then amount will be 200.

SI = A-P
SI= 100
time (t) = 10

si = (p×r×t) / 100

100 = 100×r×10/100

r = (100×100) / 100×10

r= 10

NOW SUM SHOULD BE 3 TIMES MEANS 
A= 300
now
si = A-P
si= 200

si = PRT/100

200 = (100×10×T)/100

T = (200×100)/100×10

T = 20 year


Hope it's helpful ✌✌