Question

Find the sum of first 20multiple of 9

Answer 1

Solution :-

So we have to find the sum of first 20 multiples of 9 , which is

→ 9 + 18 + 27 ..... 180

★So we can clearly see it is an AP with

• First term = 9

• Common difference = 9

• Last term = 180

★By using the formula

$\sf{ S_n = \dfrac{n}{2} (a + l)}$

$\implies \dfrac{20}{2}(9 + 180)$

$\implies\: 10(189)$

$\implies\:1890$