Class 10 NCERT Maths Solution Exercise-5.2, Arithmetic Progression(A.P).

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NCERT MATHS CLASS - X 

 Arithmetic Progressions

Exercise 5.2

Question 19:

Subba Rao started work in 1995 at an annual salary of Rs 5000 and received an increment of Rs 200 each year. In which year did his income reach Rs 7000?

The incomes that Subba Rao earned is in A.P., as every year his salary is increased by Rs 200.

Therefore, the salaries of each year from 1995

5000, 5200, 5400, …

Here, a = 5000

d = 200

Let after n^th year, his salary be Rs 7000.

Therefore, a_n = a + (n − 1) d

7000 = 5000 + (n − 1) 200

200(n − 1) = 2000

(n − 1) = 10

n = 11

Therefore, in 11th year, his salary will be Rs 7000.

Question 20:

Ramkali saved Rs 5 in the first week of a year and then increased her weekly saving by Rs 1.75. If in the n^th week, her week, her weekly savings become Rs 20.75, find n.

Given , a = 5, d = 1.75, a_n = 20.75, n = ?

In A.P. n^th term is given by

a_n = a + (n − 1) d

n − 1 = 9

n = 10

Hence, n is 10.



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