Question

find the sum of all given terma of the a.p. 4 8 12 ....20

Answer 1

Here no of terms will be 5 as seen. First term a=4,difference d= 4,last term l= 20. Sum of n terms = n/2(a+l) = 5/2(4+20) = 5/2(24) = 60

Answer 2

d= 8-4=4
a= 4
n=5
S=n{2a+(n-1)d}/2
S=4×{2×4+(5-1)4}/2
S=4×(8+16)/2
S=2×24
Sum=48