Question

Q21. If the middle term of an A.P is 15 and total no. of term is 5 then what is the
sum of first five term.
O 45
O 75
O 15
0 5
pls give the correct answer​

Answer 1

Given:

• the middle term of the A.P. is 15
• total number of terms is 5

To find: the sum of the first five terms

Solution:

• Since the A.P. contains only five terms, the middle term is the 3rd term.

• If a be the first term and d be the common ratio, then the third term is (a + 2d).

• Given, a + 2d = 15 ... ...(i)

• Sum of ghe first five terms is
• = 5/2 * [2a + (5 - 1) d]
• = 5/2 * [2a + 4d]
• = 5/2 * 2 * (a + 2d)
• = 5 * 15 [ by (i) ]
• = 75

Answer: Option 2) 75 is correct.