If k, 2k- 1 and 2k + 1 are three consecutive terms of an A.P., the value of k is

• 2

• 3

• -3

• 5

Find the number of natural numbers between 101 and 999 which are divisible by both 2 and 5.

The sum of the 2nd and the 7th terms of an AP is 30. If its 15th term is 1 less than twice its 8th term, find the AP.

In a school, students decided to plant trees in and around the school to reduce air pollution. It was decided that the number of trees, that each section of each class will plant, will be double of the class in which they are studying. If there are 1to 12 classes in the school and each class has two sections, find how many trees were planted by the students. Which value is shown in this question?

What is the common difference of an A.P. in which a₂₁- a₇= 84?

For what value of n, are the n^th terms of two A.Ps.  63, 65, 67,…. and 3, 10, 17,….. equal?

How many terms of an A.P. 9, 17, 25, …. must be taken to give a sum of 636?

If the ratio of the sum of the first n terms of two A.Ps is  (7n + 1) : (4n + 27), then find the ratio of their 9^th terms.

369.

The sum of first 20 odd natural number is

• 100

• 210

• 400

• 420

Find the sum of all three digit natural numbers, which are multiples of 7.