Latest TCS Aptitude Question SOLUTION: 17. A certain sum doubles in 7 years under simple interest. In how many years will the sum become four times itself? a) 14 b) 21 c) 28 d) NOTA

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17. A certain sum doubles in 7 years under simple interest. In how many years will the sum become four times itself?
a) 14
b) 21
c) 28
d) NOTA

Asked In TCS rajendra prasad (9 years ago)

Unsolved Read Solution (7)

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Read Solution (7) :

karisma verma  (9 years ago)

this can be solved without writing anything .Think like
Doubles in 7 years
Trebles in 14 years
4 times in 21 years

Is this solution Helpfull? Yes (10) | No (2)  

VINOD  (9 years ago)

sum double for in 7 years mean=2*(7years)=14years equivalent to 4times

Is this solution Helpfull? Yes (4) | No (5)  

AIRI RANJAN MOHANTY  (9 years ago)

ans=21

Is this solution Helpfull? Yes (2) | No   

Dilip Kumar Meghwal  (9 years ago)

Ans 14 yrs
2p=p*r*7/100
r=200/7
4p=p*(200/7)*t/100
t=14

Is this solution Helpfull? Yes (2) | No (2)  

induname  (9 years ago)

principle Amount Time
x --------> 2x(double) ------>7 years ----------->1st period
2x--------> 4x ------>7 years ----------> 2nd perios
_________
14 years
shortcut: 2x ------------> 7years
4x-------------> ?
convert 4 interms of 2(because sum is double)--------->2^2
multiplay power 2 with time 7 ----------->7*2=14
Ans:14

Is this solution Helpfull? Yes (1) | No (8)  

vinya  (9 years ago)

Answer is 21 yrs only

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Susmita Mukherjee  (5 years ago)

let sum be x,
x->2x (in 7 years) so; clearly S.I=x
(x*7*r)/100=x
or, r=100/7

now x->4x (in t yrs) clearly here S.I=3x
so (x*t*100)/(7*100)=3x
or, t=21 yrs

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