Question

An AP 5, 8, 11...has 30 terms. Find the last term. Also find the sum of the last 10terms.​

Answer 1

Answer:

Last term is 90 and sum of the last 10th term is 765.

an = 30

a= 5

n= 30

d= 3

so, a30 = a+(n-1)d

a30 = 5 +( 30-1) 3

a30 = 5 +(29)(3)

a30 = 5+ 87

a30 = 90

the last term is 90

now, sum of 10 term from Last

so, a = 90

d = -3

n = 10

A10 = 10/2{(2×90)+(10-1)-3}

A10 = 5{180+(-27) }

A10 = 765

Sum is 765