 Important for :
1
Virat has Rs. 9000. He gives this money to Mahendra on simple interest and after 4 years received the double amount. If the interest rate is 5% more than the previous, in how many years this amount will be doubled?
» Explain it
D
 S.I. = P × r × t 100

 9000 = 9000 × r × 4 100

r = 25%

New rate = 25 + 5 = 30%

9000 = 9000 × 30% × t

 t = 3 1 years 3

Hence, option D is correct.

2
Shubhranshu deposited Rs 8000 at simple interest which amounted to Rs 9200 after 3 years . Had the interest been 2% more, how much amount she would have got?
» Explain it
B
Amount = simple interest + principal

⇒ 9200 = simple interest + 8000

⇒ simple interest = 9200 – 8000

= Rs 1200

if r % be the rate of interest ,

 Then from, simple interest = principal × rate% × time 100

 1200 = 8000 × r × 3 100

⇒ r = 5%

2% more interest that is 7% interest

 simple interest = 8000 × 7 × 3 100

= Rs 1680

thus amount he will get is Rs 8000 + Rs 1680 = Rs 9680

Hence, option B is correct.

3
Rajat lends Rs. 20,000 to two of his friends. He gives Rs.10,000 to the first at 15% p.a. simple interest. Rajat wants to make a profit of 20% on the whole. The simple interest rate at which he should lend the remaining sum of money to the second friend is
» Explain it
D
Let Rajat lend the sum at x% rate to the second friend.

According to the question,

15% × 10000 + x% of 10000 = 20% of 20000

⇒  15 × 100 + 100x = 20 × 200

⇒  100x = 4000 – 1500

⇒  100x = 2500  ⇒  x = 25

Hence, the required rate of interest is 25% p.a.

Therefore, Option D is correct.

4
The SI on certain sum of money for 23 months at the rate of 7% per annum exceeds the SI on the same sum at 7% per annum for 19 months by Rs. 672. Then find the sum
» Explain it
B
Let the sum be P.

 Then, P × 7 × 23 – P × 7  × 19 = 672 12 × 100 12 × 100

or,   161P – 133P = 672 × 100 × 12

 ∴   P = 672 × 100 × 12 = Rs. 28800 28

Hence, option (B) is correct.

5
The simple interest on a sum of money will be Rs. 500 after 10 years. If the principal is made four times after 5 years, what will be the total interest at the end of the tenth year?
» Explain it
C
Given that:

Simple interest for 10 years = Rs, 500

Therefore, SI for 1 year = Rs, 50

Therefore, SI for 5 years = Rs. 250

Now, if the principal is made four times, the interest will also become four times.

Therefore, SI for next 5 years = Rs, 250 x 4 = Rs, 1000

Hence, total interest after 10 years = 250 + 1000 = Rs, 1250

Therefore, option (C) is correct.