What sum of the money will produce Rs 143 interest in years at 2.5% simple interest?
Let the required sum be Rs P.
Then, Rs P = (100 Rs 143)/ 3.25 × 2.5 = Rs 1760
A sum of money doubles itself in 10 years at simple interest. What is the rate of interest?
Let the sum be Rs 100
After 10 years it becomes Rs 200
Therefore Interest = Rs 200 – Rs 100 = Rs 100
Then, Rate = (100 × I)/ (P × T)
= (100 × 100)/ (100 × 10)
= 10%
A sum of money trebles itself in 20 years at SI. Find the rate of interest.
Rate = [100(3 – 1)]/20 = 10%
In what time does a sum of money become four times at the simple interest rate of 5% per annum?
Time
= [100(Multiple number of principal – 1)] / Rate
= [100(4 – 1)]/5 =60 years
A sum was put at SI at a certain rate for 2 years. Had it been put at 3% higher rate, it would have fetched Rs 300 more. Find the sum.
Sum
= (More Interest × 100)/ (Time × More Rate)
= (300 × 100)/ (2 × 3) = 5000
A sum of money doubles itself in 7 years. In how many years will it become fourfold?
Rate = [100(2 – 1)]/7 =100/7
Therefore Time = [100(4 – 1)]/ (100/7)
= 21 years
The simple interest on Rs 1650 will be less than the interest on Rs 1800 at 4% simple interest by Rs 30. Find the time.
We may consider that Rs (1800 – 1650) gives interest of Rs 30 at 4% per annum.
Therefore, Time = (30 × 100)/ (150 × 4) = 5 years
Bobby invested a certain sum of money at 8% p.a. simple interest for ‘n’ years. At the end of ‘n’ years, Bobby got back 4 times his original investment. What is the value of n?
Let us say Bobby invested Rs 100.
Then, at the end of ‘n’ years he would have got back Rs 400.
Therefore, the Simple Interest earned
= 400 – 100 = Rs 300.
Simple Interest = PRT/100
Substituting the values in the above equation of we get
300 = (100 × n × 8)/100
⇒ 8n = 300
⇒ n = 37.5 years.
Anita invested a certain sum of money in a bank that paid simple interest. The amount grew to Rs 240 at the end of 2 years. She waited for another 3 years and got a final amount of Rs 300. What was the principal amount that she invested at the beginning?
The sum grew to Rs 240 at the end of 2 years.
At the end of another 3 years, the sum grew to Rs 300
i.e. in 3 years, the sum grew by Rs 60
Therefore, each year, it grew by Rs 20
Sum at the end of 2 years = Rs 240
Sum grew by Rs 20 each year.
Hence, in the first 2 years, sum grew by 2 × 20 = Rs 40
Therefore, sum at the beginning of the period = Sum at the end of 2 years – Rs 40
= Rs 240 – Rs 40 = Rs 200
Pratap invested a certain sum of money in a simple interest bond whose value grew to Rs 300 at the end of 3 years and to Rs 400 at the end of another 5 years. What was the rate of interest in which he invested his sum?
Initial amount invested = Rs X
Therefore, the interest earned for the 5 years period between the 3rd year and 8th year = Rs 400 – Rs 300 = Rs 100
As the simple interest earned for a period of 5 years is Rs 100, interest earned per year = Rs 20
Therefore, interest earned for 3 years
= 3 × 20 = Rs 60
Hence, initial amount invested X
Amount after 3 years – interest for 3 years
= 300 – 60 = Rs 240
Rate of interest = (interest per year/ principal invested) × 100
= (20/240) × 100 = 8.33%
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