Question

Find the sum of the sequence 3,6,9,.....900

Answer 1

Answer:

135450

Step-by-step explanation:

3 + 6 + 9 +.......+900

3(1 + 2 +3 +.....+ 300)

3( 300 × 301/2)

135450

Answer 2

Required Sum=135450

Here,

a=3

d=6-3

=3

an=900

a+ ( n-1 ) d =900

3+ ( n-1 ) 3=900

( n-1 ) =900-3/3

( n -1)=897/3

n=299+1

n=300

Now , S n =n/2[a+an]

S n =300/2[3+900]

S n=300/2×903

S n=150×903

S n=135450