Question

which of A. P 3, 8, 16, 21 is 78?
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Answer 1

Answer:

14 th term

Step-by-step explanation:

An=a+(n-1)d

Given

An=78

a=3

d=8-3=5

=> 78=3+(n-1)5

=> 78=3+5n-5

=> 70=5n

=>n=14

Answer 2

In the given A.P the common difference is 5

and the first term is 3

Therefore if we write the general term

then t=a+(n-1)×d--------------(1)

Now, to find which term of the a.p is 78

we have to place 78 in place of "t" in the equation 1

Therefore,

78=3+(n-1)×5

78= 3+5n-5

78= 5n-2

80=5n

n=16

So, with the help of the above result we can conclude that the 16th term of the given A.P is 78.....

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