Simple interest
- A sum of money at a certain rate per annum of simple interest doubles in the 5 years and at a different rate becomes three times in 12 years. The lower rate of interest per annum is
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The sum gets doubled in 5 years and tripled in 12 years.
Clearly rate of interest for 12 years will be lower.
Let Principal be p.Then, Rate = SI × 100 Principal × Time Rate = 2p × 100 p × 12 Rate = 50 3 Rate = 16 2 % 3
Second method to solve this question :R1 = (2 - 1) × 100% = 20% 5 R2 = (3 - 1) × 100% 12
Correct Option: D
The sum gets doubled in 5 years and tripled in 12 years.
Clearly rate of interest for 12 years will be lower.
Let Principal be p.Then, Rate = SI × 100 Principal × Time Rate = 2p × 100 p × 12 Rate = 50 3 Rate = 16 2 % 3
Second method to solve this question :R1 = (2 - 1) × 100% = 20% 5 R2 = (3 - 1) × 100% 12 R2 = 16 2 % 3 ⇒ Lower rate of interest = 16 2 % 3
- At what rate of simple interest per annum will a sum become 7/4 of itself in 4 years ?
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Let the principal be p.
According to question ,∴ Principal + SI = 7p 4 ∴ SI = 7p - p = 3p 4 4 Rate = SI × 100 Principal × Time Rate = 3p × 100 = 18 3 % 4 × p × 4 4
Second method to solve this question :R = (7 / 4) - 1 × 100% = 3 × 100% 16 16
Correct Option: C
Let the principal be p.
According to question ,∴ Principal + SI = 7p 4 ∴ SI = 7p - p = 3p 4 4 Rate = SI × 100 Principal × Time Rate = 3p × 100 = 18 3 % 4 × p × 4 4
Second method to solve this question :R = (7 / 4) - 1 × 100% = 3 × 100% 16 16 R = 75 % 4 R = 18 3 % 4
- If a sum of money at simple interest doubles in 12 years, the rate of interest per annum is
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Let the principal be p.
∴Amount = 2p
∴Interest = (2p – p) = p∴ Rate = SI × 100 Principal × Time Rate = p × 100 = 25 = 8 1 % p × 12 3 3
Second method to solve this question :R = (2 - 1) × 100% 12
Correct Option: C
Let the principal be p.
∴Amount = 2p
∴Interest = (2p – p) = p∴ Rate = SI × 100 Principal × Time Rate = p × 100 = 25 = 8 1 % p × 12 3 3
Second method to solve this question :R = (2 - 1) × 100% 12 R = 25 % 3 R = 8 1 % 3
- A certain sum of money becomes three times of itself in 20 years at simple interest. In how many years does it become double of itself at the same rate of simple interest ?
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Case-I
Let the principal be P
Amount = 3P
∴ Interest = 2P
Time = 20 years∴ SI = Principal × Time × Rate 100 ⇒ 2P = P × R × 20 100
⇒ R = 10%
Case-II
SI = P
Principle = P
Rate = 10
Time = ?∴ SI = Principal × Time × Rate 100 ⇒ P = P × 10 × T 100
∴ T = 10 years.
Second method to solve this question :R% = (3 - 1) × 100% 20
R% = 10%
Correct Option: B
Case-I
Let the principal be P
Amount = 3P
∴ Interest = 2P
Time = 20 years∴ SI = Principal × Time × Rate 100 ⇒ 2P = P × R × 20 100
⇒ R = 10%
Case-II
SI = P
Principle = P
Rate = 10
Time = ?∴ SI = Principal × Time × Rate 100 ⇒ P = P × 10 × T 100
∴ T = 10 years.
Second method to solve this question :R% = (3 - 1) × 100% 20
R% = 10%Now, T = (n - 1) year R T = (2 - 1) year 10
T = 10 years
