A. 8 years
B. 10 years
C. 12 years
D. 14 years
Solution(By Examveda Team)
$$\eqalign{ & {\text{Let principal = P}} \cr & \therefore {\text{amount = 3P}} \cr & {\text{Interest = 3P}} - {\text{P}} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{\text{ = 2P}} \cr & {\text{According to the question,}} \cr & {\text{2P = }}\frac{{{\text{P}} \times {\text{R}} \times
{\text{20}}}}{{100}} \cr & \Rightarrow {\text{R = 10% }} \cr} $$
Let after t years it will become double
$$\eqalign{ & {\text{Hence,}} \cr & {\text{Interest = 2P}} - {\text{P = P}} \cr & \Rightarrow {\text{P = }}\frac{{{\text{P}} \times 10 \times {\text{t}}}}{{100}} \cr & \Rightarrow {\text{t = 10 years}} \cr} $$
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In how many years will a certain sum become 3 times itself at 25 % per annum under simple interest?a 5b 8c 12d 6
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Solution
If the sum be P.
Amount (A)=3×P=3P
Simple interest
(S.I)=A−P=3P−P=2P
Let the sum (P) be
x.
Then, simple interest
(S.I)=2x
Rate of interest
(R)=25%
Time
=T
S.I=P×R×T100
⇒T=100×S.IP×R
=100×2xx×25
=4×2
=8
Hence, 8 years required.
Hence, the correct option is (b).
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