Question

If the 3rd term in an arithmetic sequence is 10 and the sum of the 1st 6 terms is 72. The fifth term is.

Answer 1

Answer:

5th term = 18

Step-by-step explanation:

a1    +    a1+d      a1 + 2*d      a1+3d      a1 + 4*d     a1 + 5d

a1 + 2d = 10

6*a1 + 15d = 72

Multiply the first equation by 6

6a1 + 12d = 60

Write the above equation underneath the second equation

6a1  + 15d = 72

6a1 + 12d = 60                Subtract

3*d = 12                            Divide by 3

d = 12/3

d = 4

a1 + 2d = 10

a1 + 2*4 = 10

a1 + 8 = 10                        Subtract 8 from both sides

a1 - 8 = 10- 8

a1 = 2

The fifth term is

t5 = 2 + 4*4

t5 = 18