Olympiad Test: Simple Interest - 2 - Class 7 MCQ

Let the required sum be Rs P.
Then, Rs P = (100 Rs 143)/ 3.25 × 2.5 = Rs 1760

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% 

Rate = [100(3 – 1)]/20 = 10%

Time
= [100(Multiple number of principal – 1)] / Rate
= [100(4 – 1)]/5 =60 years

Sum
= (More Interest × 100)/ (Time × More Rate)
= (300 × 100)/ (2 × 3) = 5000

Rate = [100(2 – 1)]/7 =100/7
Therefore Time = [100(4 – 1)]/ (100/7)
= 21 years

We may consider that Rs (1800 – 1650) gives interest of Rs 30 at 4% per annum.
Therefore, Time = (30 × 100)/ (150 × 4) = 5 years

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.

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

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%