Question

Find the sum of first 20 positive integers divisible by 5 and 6. 10th class cbse...arithemtic progressions

Answer 1

Sum of first 20 positive integers divisible by 5 and 6 is the LCM of 5 and 6 which is 30

⇒ Sum =  First 20 multiples of 30

We know the formula,

$\boxed{\sf{S_n=\dfrac{n}{2}(x_1+x_n)}}$

Here,

• n = 20

• x₁ = 30

• xₙ = 600

$\sf{\implies S_{20} = \dfrac{20}{2}(30+600)}$

$\sf{\implies S_{20} = 10\times 630}$

$\sf{\implies S_{20} = 6300}$

$\boxed{\sf{\therefore \ Sum=6300}}$