Question

Which term of A P:3,8,13,18.....is 78?

Answer 1

Yo!

Here's the answer! :))

Given AP: 3,8,13,18....

To find: which term of this ap is 78. That is, "n".

Solution:

TN=78.

a=3.

d= t2-t1 = 8-3

= 5.

We know,

Tn= a+(n-1)d

Substituting the values we get:

78= 3+(n-1)×5.

78=3+ 5n-5.

78= –2+5n.

78+2= 5n.

80= 5n.

n= 80/5.

Therefore,

n= 16.

Hence the 16th term of this AP is 78.

Hope it helps!

–TGA.

Answer 2

Hello!!!

So, Let when the first term of AP = a

     and common difference = d

       number of terms =n

        and last term= l

   Since AP =3,8,13,18...78

 a=3

 d=(8-3)=5

 l = 78

Using the formula l=a+(n-1)d

                              78=3+(n-1)5

                          or,   78-3=5n-5

                          or,  75+5=5n

                          or, n=80/5

                          or ,n=16

So, 78 lies in 16th term of given AP.

Hope it helps !!!! :D