Some ‘interest’ing problems for police job aspirants

Hyderabad: This article is in continuation to the last article on preparation for the Sub-Inspector of Police recruitment exam. Here are some previous year questions and answers along with explanations on the Simple Interest and Compound Interest topic. 1. A bank lends Rs.30,00,000 to a person P at 12.5% simple interest and Rs.10,00,000 to another […]

Hyderabad: This article is in continuation to the last article on preparation for the Sub-Inspector of Police recruitment exam. Here are some previous year questions and answers along with explanations on the Simple Interest and Compound Interest topic.

1. A bank lends Rs.30,00,000 to a person P at 12.5% simple interest and Rs.10,00,000 to another person Q at 10.5% simple interest, for t years. If the bank received an interest of Rs.16,80,000 at the end of the period t, then t = (SI MAINS 2018)
a) 2 1/2 b) 3 c) 3 1/2 d) 4
Ans: c

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Explanation:
Simple Interest = P × T × R/ 100
Time period = t (both cases)
Given that
1680000 = (3000000 × 12.5 × t)/100 (1000000 × 10.5 × t)/100
1680000 = 375000t 105000t
1680000 = 480000t
t = 168/48 = 7/2 or 3 1/2

2. A certain sum is given on compound interest at some rate. The sum amounts to Rs 7350 and Rs 8575 at the end of 2 years and 3 years respectively. The sum given on compound interest is: (SI PRE 2018)
a) Rs 5,000 b) Rs 5,400 c) Rs 6,000 d) Rs 6,400
Ans: b

Explanation:
In compound interest the amount after this year is principle for the next year. We can consider it as simple interest for year.
SI for on Rs 7350 for 1 yr = 8575 – 7350 = Rs 1225
S.I = P × T × R/100
1225 = 7350 × 1 × R/100
R = 50/3
In compound interest A = P (1 R/100)^2
7350 = P (1 50/(3 × 100))^2
7350 = P × 7/6 × 7/6
P = 7350 × 36/49 = 5400

3. A lent Rs 5000 to B for 2 years and Rs 3,000 to C for 4 years on simple interest at the same rate of interest and received 2,200 in all form both of them as interest. The rate of interest per annum is (SI PRE 2018)
a) 10% b) 8% c) 7% d) 6%
Ans: a

Explanation:
Simple Interest = P × T × R/100
Interest rate = R% in both cases
Given that
2200 = (5000 × 2 × R)/100 (3000 × 4 × R)/100
2200 = 100R 120R
2200 = 220R
R = 10%

4. A sum of Rs 7,200 amounts to Rs 9,360 in 6 years at a certain rate of simple interest. The amount, if the rate of interest is increased by 4% is (in rupees) (SI 2016)
a) 10,080 b) 10,880 c) 11,088 d) 12,880
Ans: c

Explanation:
Simple Interest = P × T × R/100
2160 = (7200 × 6 × R)/100
R = 2160/(72 × 6) = 5
In the second case
P = 7200; R = 5 4 = 9 ; T = 6
SI = (7200 × 6 × 9)/100 = 3888
Amount = 7200 3888 = 11088

5. The present worth of Rs 132 due in two years at 5% simple interest per annum (in rupees) is (SI 2016)
a) 120 b) 122 c) 112 d) 118.80
Ans: a

Explanation:
Assume that the principle = P
S.I= P × T × R/100
Given A = 132
S.I = Amount – Principle = 132 – P
132 – P = (P × 5 × 2)/100
1320 – 10P = P
11P = 1320
P = 1320/11 = 120

6. A person borrowed a sum of money with simple interest as given below:
6% per annum for the first three years
8% per annum for the next five years
12% per annum for the next four years
If he paid a total interest of Rs 4,240, the money he borrowed (in rupees) is (SI 2016)
a) 3,000 b) 3,500 c) 4,000 d) 4,050
Ans: c

Explanation:
Let the principle = P
(P × 6 × 3/100) (P × 8 × 5/100) (P × 12 × 4/100) = 4240
18P 40P 48P = 424000
106P = 424000
P = 4000

To be continued…
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