Question

find the sum of 7+10.5+14+.....+91​

Answer 1

Answer:

4459

Step-by-step explanation:

sum of numbers=n/2(a+l)

Answer 2

Answer:

980

Step-by-step explanation:

As we know that

Sn=n/2(a+l)

than firstly we want the value of n.

91 is last term than we use formula

last term =a+(n-1)d

91=7+(n-1)d

and we know that d=10.5-7.0=3.5

and 3.5 can be written as 7/2

than

91=7+(n-1)7/2

than 7/2 go on L. H. S

182/7=7+(n-1)

26=7+(n-1)

26-7=(n-1)

19+1=n

n =20.

than putting value of n in formula of Sn, we get

Sn =20/2(7+91)

because a=7,l=91 (given)

than 10(98)

Sn =980.