Home » » In an arithmetic sequence with 25 terms, if the first term is 60 and last term i...

# In an arithmetic sequence with 25 terms, if the first term is 60 and last term i...

### Question

In an arithmetic sequence with 25 terms, if the first term is 60 and last term is -12, the sum of the terms of the sequence is

A) 600

B) 2400

C) 900

D) 1800

### Explanation:

$$-12=60 + (25-1)d$$
$$24d= -72$$
$$d=-3$$

$$s=\cfrac{n}{2}(2a + (n-1)d)$$
$$\cfrac{25}{2}(2 \times 60 + (25-1)-3)$$
$$\cfrac{25}{2}(120-72)$$
$$\cfrac{25}{2}(48)$$
$$=600$$

Explanation provided by Uwakwe Chukwuemeka

## Discussion (2)

• Uwakwe Chukwuemeka

$$-12=60 + (25-1)d$$
$$24d= -72$$
$$d=-3$$

$$s=\cfrac{n}{2}(2a + (n-1)d)$$
$$\cfrac{25}{2}(2 \times 60 + (25-1)-3)$$
$$\cfrac{25}{2}(120-72)$$
$$\cfrac{25}{2}(48)$$
$$=600$$