NCERT Solution Class 8th Maths Chapter – 7 Comparing Quantities Exercise – 7.3

NCERT Solution Class 8th Maths Chapter - 7 Comparing Quantities Exercise - 7.3
Last Doubt

NCERT Solution Class 8th Maths Chapter – 7 Comparing Quantities

TextbookNCERT
Class 8th
Subject Mathematics
Chapter7th
Chapter Name Comparing Quantities
CategoryClass 8th Maths
Medium English
SourceLast Doubt

NCERT Solution Class 8th Maths Chapter 7 Comparing Quantities

Chapter – 7

Comparing Quantities

Exercise – 7.3

Q1. The population of a place increased to 54,000 in 2003 at a rate of 5% per annum.

(i) Find the population in 2001.
(ii) What would be its population is 2005?

Ans – Population in 2003 is P = 54000

(i) Let the population in 2001 (i.e. 2 years ago) = P
Since rate of increment in population = 5% p.a.

∴ Present population = p(1+5\100)

or 54000 = p(21\20)2

or 54000 = p(441\400)

or p = 54000 x 400 \441 =48979.59

= 48980 (approx.)

Thus, the population in 2001 was about 48980.

(ii) Initial population (in 2003), i.e. P = 54000

Rate of increment in population = 5% p.a.
Time = 2 years ⇒n = 2

∴ A = p(1+R\100)2
5400(1+5\100)2 = 5400 x21\20 x21\20

= 135 * 21 * 21 = 59535
Thus, the population in 2005 = 59535.

Q2. In a laboratory, the count of bacteria in a certain experiment was increasing at the rate of 2.5% per hour. Find the bacteria at the end of 2 hours if the count was initially 5,06,000.

Ans- Initial count of bacteria (P) = 5,06,000
Increasing rate (R) = 2.5% per hour
Time (T) = 2 hour. ⇒ n = 2

A =P(+R\100)n

A = 506000(1+2.5\100)2= 506000 (1+25\1000)2

= 506000 (41\40)2 = 506000 x 41\40x 41\40

= 6325x41x41 \20 =10632325\20

= 531616.25 or 531616 (approx.)

Thus, the count of bacteria after 2 hours will be 531616 (approx.).

Q3. A scooter was bought at ₹ 42,000. Its value depreciated at the rate of 8% per annum. Find its value after one year.

Ans – Initial cost (value) of the scooter (P) = Rs 42000
Depreciation rate = 8% p.a.
Time = 1 year ⇒ n = 1

Using A = P(1+R\100)n,We have

A= Rs 42000 x(1-8\100)1
= Rs 42000 x92\100
= ₹ 420 × 92 = ₹ 38640

Thus, the value of the scooter after 1 year will be ₹ 38640.