Question

In an a.p if the 7th term is 10and 10th term is 7.find the 20th term

Answer 1

Answer:

See the attachment for answer

Answer 2

Given:

In an a.p the 7th term is 10and 10th term is 7.

To find:

Find the 20th term

Solution:

From given, we have,

In an a.p the 7th term is 10and 10th term is 7.

we use the formula,

Tn = a + (n - 1) d

where a = first term

d = common difference

n = nth term

T7 = a + (7 - 1)d = 10

a + 6d = 10 .......(1)

T10 = a + (10 - 1)d = 7

a + 9d = 7 .......(2)

solving equations (1) and (2), we get,

-3d = 3

d = -1

substituting the value of d in one of the equations, we get,

a + 6 (-1) = 10

a - 6 = 10

a = 16

The 20th term is given as,

T20 = 16 + (20 - 1) (-1)

T20 = 16 + (19) (-1)

T20 = 16 - 19

T20 = - 3

Therefore, the value of 20th term is -3.