# CBSE Class 10-Mathematics: Chapter –5 Arithmetic Progressions Part 4

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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,