Question

If 5th term and 12th term of an AP are 30 and 65 respectively what is sum upto 20 term?

Answer 1

answer is attached in file

Answer 2

hi

the formula for the nth term is,

an= a0 + (n-1)* d

a5 = a0 +(5-1) *d = 30 ---->(1)  a0 + 4d = 30

a12 = a0 + (12 -1) *d =65 ---->(2) = a0 + 11d = 65

substituting (1) in (2)

30 + 7d = 65

7d = 35

d= 5

the sum of n terms is

sn = n/2[2a0 + (n-1) d]

a0 = d =5

s20 = 20/2[2(5) + (20 -1 )5]

= 10 [ 10 + 19*5]

= 10 [10 + 95]

= 1050

hope this helps.....