Unit-2: commercial mathematics
(a) Compound interest and simple interest
(b) Profit, loss and discount
Q1.
Find the interest on Rs.600 at 6% per annum for 46days .
(a) 16 (b) 15 (c) 14 (d) 14.40
Solution.
S.I =
prt/100
= 600 x
6/100
146/365
= 14.40
Note: t= time always taken in years so convert days into year.
Solution
Q2.
Mr A invested Rs. 3500 for 6 years Rs. 4000 for 4 years at the same rate of simple interest. He received a total simple interest
of Rs 2700. Find the rate.
(a) 7.3% (b) 8% (c) 8.2% (d) 9%
Solution.
SI =
3500 x 6 x R/100
+
4000 x 4 x R/100
2700 = 210R + 160R
2700 = 370R
R =
2700/370
= 7.3%
Solution
Q3.
Find the ratio of simple interest earned by certain amount at the same rate of interest for 9 years and 15 years .
(a) 3:5 (b) 3:2 (c) 2:5 (d) 2:3
Solution.
Let certain amount is P and rate of interest is R .
Required Ratio = (PR.9/100)/(PR.5/100)
= 9/15
= 3:5
Solution
Q4.
If a certain amount becomes double in 8 years at a simple interest. In how many years it will be four times?
(a) 21 yrs (b) 20 yrs (c) 24 yrs (d) 30 yrs
Solution.
P =
p x 8r/100
r = 12.5%
3P =
p x 12.5 x t/100
t = 24 yrs.
Solution
Q5.
In what time will Rs.8000 amount to Rs.8820 at 10% per annum interest compounded half-yearly.
(a) 1 (b) 2 (c) 3 (d) 4
Solution.
i =
10/2
% = 5%
A = P(1+i)
n 8820 = 8000 (1.05)
2n n = 1 yrs.
Solution
Q6.
The difference between simple interest and compound interest on Rs.1250 for 2 years at 8% p.a. is .
(a) 13 (b) 12.5 (c) 12 (d) 14
Solution.
C.I - S.I = P(R/100)2
= 1250 x (10/100)2
= 1250/100
= 12.5
Solution
Q7.
If a man purchased 11 toffees for Rs.10 and sells 10 toffees for Rs.11,How much profit he will make .
(a) 18% (b) 19% (c) 21% (d) 20%
Solution.
Purchase 11 toffees for Rs.10
Sale 10 toffees for Rs.11
= (121-100/100) x 100
= 21%
Solution
Q8.
A person purchased mobile for Rs.1850. For how much should he sell it gain 10% ?
(a) 2035 (b) 2000 (c) 1890 (d) 2050
Solution.
SP = (100 + 10)% of C.P
SP = 110% of C.P
SP = 110/100 x 1850
= 2035
Solution
Q9.
A sells a good to B at a profit of 20% and B sells it it C at a profit of 25% . If C pays Rs.500 for it, what did A pay for it.
(a) Rs.400 (b) Rs.394 (c) Rs.334 (d) Rs.500
Solution.
Trick = a + b + ab/100
a and b are profit percentage
= 20 + 25 + 500/100 = 50%
Rs.334
Solution
Q10.
A student sold a book at a profit of of 12%. If he sold it for Rs.30 more, then he gained 18% . Find the cost price .
(a) Rs 200 (b) Rs 300 (c) Rs 400 (d) Rs 500
Solution.
18% of cost - 12% of cost = Rs 30
6% of cost = Rs 30
cost price = 30 x 100/6 = 500
Solution
