Question

find the sum of senies 4+12+20+28+.......100​

Answer 1

Answer:

20200

Step-by-step explanation:

Here,a=4 ,b=12-4=8,n=100

So,S100=100/2[2*4+99*4]=50*[404]=20200

Answer 2

an= a+( n-1)d

100=4+( n-1)8

96=(n-1)8

96/8= n-1

12= n-1

n=12+1

n=13

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

sn=13/2[2(4)+(13-1)8]

sn=13/2[8+96]

sn=13/2(104)

sn=1352/2

sn=676