Sum of n terms of an A.P. whose first term is a and common difference is d, is given by:

1. S_n = $\dfrac{n}{2}[a + (n − 1)d]$

2. S_n = $\dfrac{n}{2}[2a + (n + 1)d]$

3. S_n = $\dfrac{n}{2}[2a − (n − 1)d]$

4. S_n = $\dfrac{n}{2}[2a + (n − 1)d]$

Sum of n terms of an A.P. whose first term and last term are a and l respectively is given by:

1. S_n = $\dfrac{n}{2}(a + l)$

2. S_n = $\dfrac{n}{2}(a − l)$

3. S_n = $\dfrac{n}{2}(2a + l)$

4. S_n = $\dfrac{n}{2}[a + (n − 1)l]$

The sum of first 50 natural numbers is:

1. 1050

2. 1175

3. 1225

4. 1275

The nth term of an Arithmetic Progression (A.P.) is 2n + 5. The 10th term is :

1. 7

2. 15

3. 25

4. 45