NCERT Class X Chapter 5: Arithmetic Progression Exercise 5.1 Question 1(ii)

NCERT Class X Chapter 5: Arithmetic Progression Exercise 5.1 Question 1 (ii)

Question:

In which of the following situations, does the list of numbers involved make an arithmetic progression, and why? 

The amount of air present in a cylinder when a vacuum pump removes 1/4 of the air remaining in the cylinder at a time.

Given:

A vacuum pump removes 14 of the remaining air in a cylinder at a time.

To Find:

Whether the amounts of air remaining after each pump form an arithmetic progression.

Formula:

An arithmetic progression is a sequence where the difference between consecutive terms is constant.

Solution:

For every use the vacuum pump removes  14 x air present inside cylinder  

Let the initial amount of air be A.

After the first pump, the remaining air is A - (14 A) = 34 A.

Now the air inside the cylinder is  34 A.

After the second pump, the remaining air is (34A) - (14 (34 A)) 

= (34 A) - ((316A)) 

= 12 - 316 A

916 A

= (34)2A.

The sequence is A, 34A, (34)2A, ... This is not an arithmetic progression since the difference between the terms are not a constant.

Result:

The amounts of air remaining do not form an arithmetic progression.

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