If the sum of first n terms of an A.P. is S_n = 5n² + 3n, then its common difference is:

1. 8

2. 10

3. 18

4. 26

The first and the last terms of an A.P. are 1 and 11 respectively. If the sum of its terms is 36, then the number of terms is :

1. 6

2. 7

3. 8

4. 9

The sum of first 30 odd natural numbers is:

1. 800

2. 900

3. 729

4. 1249

The 7th term of an A.P. is 4 and its common difference is −4. The first term of the A.P. is :

1. 32

2. 28

3. 24

4. 36