Question

The fifth term is40 and tenth term is20find fifteenth term

Answer 1

Answer:

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Answer 2

Given:-

The fifth term is 40.

=> t5 = 40

Tenth term is 20.

=> t10 = 20

To find:-

fifteenth term, i.e. t15 = ?

Solution:-

t5 = 20, t10 = 20

now,

tn = a + (n - 1)d

t5 = a + (5 - 1)d

40 = a + 4d

a + 4d = 40 .....(1)

similarly,

t10 = a + (10 - 1) d

20 = a + 9d

a + 9d = 20 .....(2)

• Substracting the eq (2) from (1)

a + 4d = 40

- (a + 9d = 20)

=> -5d = 20

d = 20/-5 = -4

d = -4

• Substituting d = 4 in eq (1)

a + 4d = 40

a + 4 (-4) = 40

a - 16 = 40

a = 40 + 16 = 56

a = 56

now,

t15 = a + (n - 1)d

t15 = 56 + (15 - 1)-4

t15 = 56 + (14)-4

t15 = 56 - 56

t15 = 0

Answer

Fifteenth term is 0