Question

Find the 8th term of an AP whose first term is - 24 and 11th term is 21.




​

Answer 1

Answer: 7.5

Step-by-step explanation:

• Given 1st term a=-24 and 11th term a+10d=21.
• Putting the value of a in the 11th term
• -24 + 10d=21

    ⇒10d=21+24

    ⇒10d=45

    ∴ d=4.5

• So, 8th term of an AP is given by a+7d

                                                            = -24+ 7*4.5

                                                            = -24 + 31.5

                                                            = 7.5

Answer 2

The $8^{th}$ term is 7.5

Given:

The value of first term is -24 and the eleventh term is 21.

To find:

The value of $8^{th}$ term

Solution:

We know,

$n^{th}$ term= a+(n-1)d......... equation 1

where a is first term

n is the number of terms,

d is the common difference

To find common difference (d); put the values in equation 1

The given term is $11^{th}$,

So,

$11^{th}$ term= -24+(11-1)d

21=-24+10d...( by equation 1)

10d=45

d= 4.5.

$8^{th}$ term= -24+(8-1)d

=-24+7(4.5)

=-24+31.5

=7.5

Hence; The value of $8^{th}$ term is 7.5.