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.

NCERT - Mathematics

Book: NCERT - Mathematics

Chapter: 8. Comparing Quantities

Subject: Maths - Class 8^th

Q. No. 11 of Exercises 8.3

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11

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.

This problem can be solved on the basis of CI problems.

Let principal (P) = 5,06,000, Rate of Interest (R) = 2.5%, Time, n = 2 hours

After 2 hours, number of bacteria, =

= 5,31,616.25

Hence, number of bacteria after two hours are 531616 (approx.)

11

Chapter Exercises

Exercises 8.1

Exercises 8.2

Exercises 8.3

1

Calculate the amount and compound interest on
(a) Rs 10,800 for 3 years at per annum compounded annually.

(b) Rs 18,000 for years at 10% per annum compounded annually.

(c) Rs 62,500 for years at 8% per annum compounded half yearly.

(d) Rs 8,000 for 1 year at 9% per annum compounded half yearly.

(You could use the year by year calculation using SI formula to verify).

(e) Rs 10,000 for 1 year at 8% per annum compounded half yearly.

2

Kamala borrowed Rs 26,400 from a Bank to buy a scooter at a rate of 15% p.a. compounded yearly. What amount will she pay at the end of 2 years and 4 months to clear the loan?

3

Fabina borrows Rs 12,500 at 12% per annum for 3 years at simple interest and Radha borrows the same amount for the same time period at 10% per annum, compounded annually. Who pays more interest and by how much?

4

I borrowed Rs 12,000 from Jamshed at 6% per annum simple interest for 2 years. Had I borrowed this sum at 6% per annum compound interest, what extra amount would I have to pay?

5

Vasudevan invested Rs 60,000 at an interest rate of 12% per annum compounded half yearly. What amount would he get
(i) after 6 months?

(ii) after 1 year?

6

Arif took a loan of Rs 80,000 from a bank. If the rate of interest is 10% per annum, find the difference in amounts he would be paying after years if the interest is
(i) compounded annually.

(ii) compounded half yearly.

7

Maria invested Rs 8,000 in a business. She would be paid interest at 5% per annum compounded annually. Find
(i) The amount credited against her name at the end of the second year.

(ii) The interest for the 3rd year.

8

Find the amount and the compound interest on Rs 10,000 for years at 10% per annum, compounded half yearly. Would this interest be more than the interest he would get if it was compounded annually?

9

Find the amount which Ram will get on Rs 4096, if he gave it for 18 months at per annum, interest being compounded half yearly.

10

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 in 2005?

11

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.

12

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