Find the sum of first 15 multiples of 8? [with Video] - Teachoo

Ex 5.3, 13 - Chapter 5 Class 10 Arithmetic Progressions - Part 2

Learn in your speed, with individual attention - Teachoo Maths 1-on-1 Class


Transcript

Ex 5.3, 13 Find the sum of first 15 multiples of 8. Multiples of 8 are 8, 16, 24,… Since difference is same, it is an AP We need to find sum of first 15 multiples We use formula Sn = 𝑛/2 (2𝑎+(𝑛−1)𝑑) Here, n = 15, a = 8 & d = 16 – 8 = 8 Putting values in formula Sn = 𝒏/𝟐 (𝟐𝒂+(𝒏−𝟏)𝒅) = 15/2(2 × 8+(15−1) × 8) = 15/2 (16+14 × 8) = 15/2 (16+112) = 15/2 × 128 = 960 Therefore, the sum of first 15 multiples of 8 is 960

Ask a doubt
Davneet Singh's photo - Co-founder, Teachoo

Made by

Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.