Question

Find the sum
a)3+6+9+..120
b)13599
c)51015400​

Answer 1

Answer:

1230

Step-by-step explanation:

given series 3+6+9..120 is in am

last element(l) =120

first element (a)=3

common diff(d) =3

n=20

sum of series in am= n/2 × ( a + l)= 20/2 ×(3+120)

= 10(123) = 1230

if last term is not given sum will be n/2 ×( 2a + (n-1)d)