# CBSE Class 10-Mathematics: Chapter – 5 Arithmetic Progressions Part 4 (For CBSE, ICSE, IAS, NET, NRA 2022)

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**Question 17**:

If are in AP find

**Answer**:

are in AP find .

On solving we get

**Question 18**:

Find the middle term of the AP

**Answer**:

Middle terms

term is middle term

**Question 19**:

Find the common difference of an AP whose first term is and sum of whose first terms is times the sum of next terms.

**Answer**:

APQ

**Question 20**:

Find the sum of all-natural no. between & which are divisible by . Find their sum.

**Answer**:

No let and , which are divisible by .

No. which are divisible by are

No. which are divisible by

There are terms between divisible by .

**Question 21**:

The ratio of the sum of first terms of two AP՚s is . Find the ratio of their terms

**Answer**:

Let be the I terms are of two AP՚s

We have sub,