# Selina Concise Solutions for Chapter 10 Simple Interest Class 7 ICSE Mathematics

**Exercise 10**

**1. Find the S.I. and amount on :**

**(i) Rs. 150 for 4 years at 5% per year.(ii) Rs. 350 foryears at 8% p.a.(iii) Rs. 620 for 4 months at 8 p. per rupee per month.(iv) Rs. 3,380 for 30 months at% p.a.(v) 600 from July 12 to Dec. 5 at 10% p.a.(vi) Rs. 850 from 10th March to 3rd August at% p.a.(vii) Rs. 225 for 3 years 9 months at 16% p.a.**

**Answer **

**(i)** P = Rs. 150, R = 5% per year , T = 4 years

**2. On what sum of money does the S.I. for 10 years at 5% become Rs. 1,600 ?**

**Answer**

S.I. = Rs. 1600, R = 5% p.a.

T = 10 years

T = 10 years

**3. Find the time in which Rs. 2,000 will amount to Rs. 2,330 at 11% p.a. ?**

**Answer**

Amount (A) = Rs. 2330

Principal (P ) = Rs. 2000

∴ S.I. = A - P = Rs. 2330 - Rs. 2000 = Rs. 330

R = 11% p.a.

Principal (P ) = Rs. 2000

∴ S.I. = A - P = Rs. 2330 - Rs. 2000 = Rs. 330

R = 11% p.a.

**4. In what time will a sum of money double it self at 8% p.a ?**

**Answer**

Let the principal (P) = ₹ 100

∴ Amount (A) = ₹ 100×2 = ₹ 200

∴ S.I. = A - P = ₹ 200 - ₹ 100 = ₹ 100

Rate(R) = 8% p.a.

∴ Amount (A) = ₹ 100×2 = ₹ 200

∴ S.I. = A - P = ₹ 200 - ₹ 100 = ₹ 100

Rate(R) = 8% p.a.

**5. In how many years will be ₹870 amount to ₹1,044, the rate of interest being 2% p.a ?**

**Answer**

Principal (P) = ₹ 870

Amount (A) = ₹ 1044

∴ S.I. = P - A = ₹ 1044 - ₹ 870 = ₹ 174

Amount (A) = ₹ 1044

∴ S.I. = P - A = ₹ 1044 - ₹ 870 = ₹ 174

**6. Find the rate percent if the S.I. on ₹ 275 is 2 years is ₹ 22.**

**Answer**

Principal (P) = ₹ 275, S.I. = ₹ 22

Time = 2 years

Time = 2 years

**7. Find the sum which will amount to ₹700 in 5 years at 8% rate p.a.**

**Answer**

Amount = ₹ 700, Rate (R) = 8% p.a.

Time(T) = 5 years

Let principal (P) = ₹ 100

Time(T) = 5 years

Let principal (P) = ₹ 100

∴ Amount (A) = P + S.I.

= ₹ 100 + 40 = ₹140

If amount is ₹ 140, then principal = ₹ 100

and, if amount is Rs. 700, then principal

= ₹ 100 + 40 = ₹140

If amount is ₹ 140, then principal = ₹ 100

and, if amount is Rs. 700, then principal

**8. What is the rate of interest, if ₹3,750 amounts to ₹4,650 in 4 years ?**

**Answer**

Principal (P) = ₹ 3750

Amount (A) = ₹ 4650

∴ S.I. = A - P = ₹ 4650 - 3750 = ₹ 900

Time (T) = 4 years .

Amount (A) = ₹ 4650

∴ S.I. = A - P = ₹ 4650 - 3750 = ₹ 900

Time (T) = 4 years .

**9. In 4 years, ₹6,000 amount to ₹8,000. In what time will ₹525 amount to ₹700 at the**

**same rate ?**

**Answer**

In first case, Principal (P) = ₹ 6000

Amount (A) = ₹ 8000

∴ S.I. = A - P = ₹ 8000 - ₹ 6000 = ₹ 2000

Time(T) = 4 years

Amount (A) = ₹ 8000

∴ S.I. = A - P = ₹ 8000 - ₹ 6000 = ₹ 2000

Time(T) = 4 years

**Answer**

Let the sum (P) = Rs. 100

**11. What sum of money lent out at 5% for 3 years will produce the same interest as**

**Rs. 900 lent out at 4% for 5 years ?**

**Answer**

In second case, Principal (P) = Rs. 900

Rate(R) = 4%, Time(T) = 5 years

Rate(R) = 4%, Time(T) = 5 years

**12. A sum of Rs. 1,780 become Rs. 2,136 in 4 years,**

**Find :**

**(i) the rate of interest.**

**(ii) the sum that will become Rs. 810 in 7 years at the same rate of interest ?**

**Answer**

**(i)**In first case, Principal (P) = Rs, 1780

Amount(A) = Rs. 2136

∴ S.I. = A - P = Rs. 2136 - 1780 = Rs. 356

Time (T) = 4 years

**(ii)**In second case, Let principal (P) = Rs. 100

Rate(R) = 5% p.a., Time(T) = 7 years

∴ Amount = P + S.I. = Rs. 100 + 35 = Rs. 135

If amount is Rs. 135, then principal = Rs. 100

and if amount is Rs. 810, then principal

**13. A sum amounts to Rs. 2,652 in 6 years at 5% p.a. simple interest.**

**Find :**

**(i) the sum**

**(ii) the time in which the same sum will double itself at the same rate of interest.**

**Answer**

**(i)**In first case, Let principal (P) = Rs. 100

Rate(R) = 5% p.a. , Time (T) = 6 years

and, amount = Rs. 100 + Rs. 30 = Rs. 130 If amount is Rs. 130, then principal = Rs. 100

and, if amount is Rs. 2652, then principal

In second case, Let sum (P) = Rs. 100

Amount (A) = Rs. 100× 2 = Rs. 200

S.I. = A - P = Rs. 200 - 100 = Rs. 100

Rate = 5% p.a.

**14. P and Q invest Rs. 36,000 and Rs. 25,000 respectively at the same rate of interest**

**per year. If at the end of 4 years, P gets Rs. 3,080 more interest than Q; find the**

**rate of interest.**

**Answer**

P's investment (P

and Q's investment (P

Period(T) = 4 years, Let rate of interest = x %

Difference in their interest _{1}) = Rs. 36000and Q's investment (P

_{2}) = Rs. 25000Period(T) = 4 years, Let rate of interest = x %

= Rs. (1440 - 1000)x = Rs. 440x

But difference = Rs. 3080

∴ 440x = 3080 ⇒ x 3080/440 ⇒ x = 7%

∴ Rate of interest = 7% p.a.

**15. A sum of money is lent for 5 years at R% simple interest per annum. If the interest**

**earned be one-fourth of the money lent, find the value of R.**

**Answer**

**16. The simple interest earned on a certain sum in 5 years is 30% of the sum. Find the**

**rate of interest.**

**Answer**

Let the sum (P) = ₹100