Question

if 5,10,15,.....150 is the given AP find n, t 20 and Sn​

Answer 1

Answer:

a= 5 d=5 an=150 put it in formula of an=a+(n-1)d

and in sn formula

Answer 2

Answer:

n=30 , T(20) or A(20)=100 , S(n)=387.5

Step-by-step explanation:

A.P= 5,10,15,...150

A(n)=150

a=5

d=10-5=5

n=?

S(n)=?

T(20) or A(20)=?

ATQ:

A(n)=a+(n-1)d

150=5+(n-1)5

150=5+5n-5

150=5n

n=30

Now,

A(n)=a+(n-1)d

A(20)=5+(20-1)5

A(20)=5+100-5

A(20)=100

Then,

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

S(n)=5/2[2(5)+(30-1)5]

S(n)=5/2[10+(29)5]

S(n)=5/2[10+145]

S(n)=5/2[155]

S(n)=775/2

S(n)=387.5

hence, n=30 , T(20) or A(20)=100 , S(n)=387.5

hope it helps :)