Exercise 8D
Question 1
Find the simple interest and the amount of simple interest of
(a) Rs. 350 for 3 years at 6%
Sol :
$I=\frac{\text{PRT}}{100}=\frac{350\times 6\times 3}{100}$
=63
(b) Rs. 765 for 2 1 by 2 years at 5 1 by 3 percent
Sol :
P=765
$T=2\frac{1}{2}=\frac{5}{2}$y
$R=5\frac{1}{3}=\frac{16}{3}$%
I=?
$I=\frac{\text{PRT}}{100}=\frac{765\times \frac{16}{3}\times \frac{5}{2}}{100}$
$=\frac{765\times 16\times 5}{100\times 3\times 2}$
=102
∴Total amount of simple interest=102+765
=867
(c) Rs. 475 for 2 years 4 months at 4 and 1 by 2 percent.
Sol :
P=475
$R=4\frac{1}{2}=\frac{9}{2}$%
T=2year 4month
$=2+\frac{4}{12}$
$=2+\frac{1}{3}=\frac{7}{3}$
$I=\frac{\text{PRT}}{100}=\frac{475\times 9\times 7}{100\times 2\times 3}$
∴Amount simple interest
=48.875+475
=524.875
(d) Rs. 1900 for 20 months at 6%
Sol :
P=1900 , R=6%
$I=\frac{\text{PRT}}{100}=\frac{1900\times 6\times 5}{100\times 3}$
=190
∴Total I=190+1900=2090
(e) Rs. 7300 for April 5 to June 24 at 5%
Sol :
P=7300 , R=5%
T=5th april to 2 years $=\frac{80}{365}$years
$I=\frac{\text{PRT}}{100}=\frac{7300\times 5\times 80}{100\times 365}$
=80
∴Total I=7300+80
=7380
Question 2
Find the rate per cent p.a. when Rs. 800 yields Rs. 80 interest in 2 years.
Sol :
$I=\frac{\text{PRT}}{100}$
or $R=\frac{100I}{\text{PT}}=\frac{100\times 80}{800\times 2}$
=5%
Question 3
In what times Rs. 600 will yield Rs. 48 interest at 4% p.a.?
Sol :
P=600, I=48 , R=4%
$T=\frac{I100}{PR}=\frac{48\times 100}{600\times 4}$
=2 year
Question 4
Find what sum of money will yield Rs. 231 interest in 3 years at 7% p.a.
Sol :
I=231 , T=3 year, R=7%
⇒$I=\frac{\text{PRT}}{100}$
$P=\frac{I\times 100}{RT}$
$P=\frac{231\times 100}{3\times 7}$
=1100
This is very good
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