Question

The sum first 9 term of an arithmetic sequence is 90. What is its 5th term

Answer 1

Answer:

it's 50 because if it is 9 term than 90 then 5 means 50 and if this is wrong the sorry because I am studying in 7th STD only

Answer 2

Given ,

The sum first 9 term of an arithmetic sequence is 90

We know that , the sum of first n terms of an AP is given by

$\boxed{ \sf{S_{n} = \frac{n}{2} \{2a + (n - 1)d \}}}$

Thus ,

$\sf \mapsto 90 = \frac{9}{2} \{ 2a + (9 - 1)d \} \\ \\ \sf \mapsto 90 = \frac{9}{2} (2a + 8d) \\ \\\sf \mapsto 10 = \frac{2}{2} (a + 4d) \\ \\\sf \mapsto a + 4d = 10$

Now , the 5th term will be

a + (5 - 1)d

a + 4d

10

Therefore ,

• The 5th term of AP is 10