Simple Interest Questions - 1

Find the amount payable on a sum of Rs.15000, simple interest at 15% p.a. for three years ?
• Rs.16750
• Rs.21750
• Rs.20000
• Rs.18000
• Rs.22000
Explanation

S.I = $\displaystyle \frac{15000 \times 15 \times 3}{100}$ = Rs.6750.

Amount = Principal + interest = Rs.15000 + Rs.6750 = Rs.21750.

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Find the amount payable on a sum of Rs.24000, simple interest at 12% p.a. for 18 months ?
• Rs.33000
• Rs.32500
• Rs.34600
• Rs.28320
• Rs.27800
Explanation

S.I = $\displaystyle \frac{{24000 \times 12 \times 1\frac{1}{2}}}{100} = \frac{{24000 \times 12 \times \frac{3}{2}}}{100}$ = Rs.4320.

Amount = Principal + interest = Rs.24000 + Rs.4320 = Rs.28320.

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An amount becomes 1.5 times of its principal in 4 years. Find the rate of interest ?
• 15% p.a.
• 10% p.a.
• 12.5% p.a.
• 18% p.a.
• 21% p.a.
Explanation

Let the amount be 100.

Amount after 4 years = 100 x 1.5 = 150.

Interest = Total amount â€“ Principal = 150 â€“ 100 = 50.

Rate = $\displaystyle \frac{50}{4}$ = 12.5%.

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A person lent Rs.15000 each to two persons A and B, at simple interest, to A at 15% p.a. and to B at 12% p.a. After what least time interest payable by B equals to interest paid by A ?
• 4 years
• 5 years
• 6 years
• 3 years
• 7 years
Explanation

Find the LCM of 15 and 12 => 60.

The rate of interest at 15% becomes 60% in => $\displaystyle \frac{60}{15}$ = 4 years.

The rate of interest at 12% becomes 60% in => $\displaystyle \frac{60}{12}$ = 5 years.

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A sum amounts to Rs.32500 in two years, to Rs.43750 in 5 years. Find the sum ?
• Rs.23000
• Rs.24000
• Rs.26000
• Rs.25000
• Rs.22500
Explanation

The sum in:

 Â 5 years Â = Â Rs.43750 Â Â Â Â Â 2 years Â = Â Rs.32500 Â Â Â Â Diff Â 3 years Â = Â Rs.11250 Â Â Â Â Â

For each year = $\displaystyle \frac{11250}{3}$ = 3750.

Total interest = 3750 x 5 = 18750.

Principal = 43750 â€“ 18750 = Rs.25000.

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Find Principal, if interest paid Rs.10800, simple interest 12% p.a. for 3 years ?
• Rs.30000
• Rs.25000
• Rs.18000
• Rs.28000
• Rs.36000
Explanation

Principal = $\displaystyle \frac{\text{Simple Interest}}{\text{Rate} \times \text{Time}} \times 100$

Principal = $\displaystyle \frac{10800}{12 \times 3} \times 100$ = Rs.30000.

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Find Rate of interest, if time is 3 years, Principal is Rs.18000, simple interest paid is Rs.8100 ?
• 14% p.a.
• 12% p.a.
• 16% p.a.
• 10% p.a.
• 15% p.a.
Explanation

Rate = $\displaystyle \frac{\text{Simple Interest}}{\text{Principal} \times \text{Time}} \times 100$

Rate of interest = $\displaystyle \frac{8100}{18000 \times 3} \times 100$ = 15 or 15%.

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Find time, if rate of interest is 18%, Principal is Rs.25000, Simple interest paid is Rs.18000 ?
• 5 years
• 4 years
• 3 years
• 2 years
• 6 years
Explanation

Time = $\displaystyle \frac{\text{Simple Interest}}{\text{Principal} \times \text{Rate}} \times 100$

Time = $\displaystyle \frac{18000}{25000 \times 18} \times 100 = \frac{100}{25}$ = 4 years.

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Find simple interest on Rs.14600, at 10% p.a. for 125 days [of 365 days] ?
• Rs.1460
• Rs.7300
• Rs.500
• Rs.600
• Rs.700
Explanation

Simple interest = $\displaystyle \frac{14600 \times 10 \times \frac{125}{365}}{100}$ = 500.

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Equal sum of money were lent to X and Y, for 2 years and 9 months, and 3 years and 4 months respectively both at 12% p.a. simple interest. The difference between the interests paid by them is Rs.1050. find Principal ?
• Rs.7500
• Rs.12000
• Rs.14000
• Rs.15000
• Rs.10500
Explanation

Principal = P, Rate = 12%, Time = 2 years 9 months = $\displaystyle \frac{2.9}{12} = \frac{11}{4}$ years or $\displaystyle \frac{33}{36}$ months.

Interest paid by X = $\displaystyle \frac{{\text{P} \times 12 \times \frac{11}{4}}}{100} = \frac{33P}{100}$

Time for Y = 3 years 4 months = $\displaystyle \frac{3.1}{3}$ years = $\displaystyle \frac{10}{3}$ years or $\displaystyle \frac{40}{48}$ months.

Interest paid by Y = $\displaystyle \frac{{\text{P} \times 12 \times \frac{10}{3}}}{100} = \frac{4\text{P}}{100}$

=> $\displaystyle \frac{4\text{P}}{100} - \frac{33\text{P}}{100} = 1050 => \frac{40\text{P} â€“ 33\text{P}}{100}$ = 1050.

=> 7P = 105000 => P = $\displaystyle \frac{105000}{7}$ = 15000.

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Simple Interest Important Formulas

Principal: The money borrowed or lent out.

Interest: extra money paid or received on principal.

Simple interest is a rate of percent that calculated on principal only.

Simple Interest Important Rules:

Simple Interest = $\displaystyle \frac{\text{P} \times \text{T} \times \text{R}}{100}$

P = Principal;     T = Time;    R = Rate of Interest.

Principal = $\displaystyle \frac{\text{Simple Interest}}{\text{Rate} \times \text{Time}} \times 100$

Rate = $\displaystyle \frac{\text{Simple Interest}}{\text{Principal} \times \text{Time}} \times 100$

Time = $\displaystyle \frac{\text{Simple Interest}}{\text{Principal} \times \text{Rate}} \times 100$

Time: