Question

I need some help please with this

Answer 1

a) 4005

b) 1010025

c) 15150

d) 50500

Explanation:

let me explain the first one

let s = the sum of the numbers

s = 1 + 2 + 3 + ... + 87 + 88 + 89 Equation1

or we can rewrite the equatio1 like this

s = 89 + 88 + 87 + ... +3 + 2 + 1 Equation 2

Add equations 1 and 2

s = 1 + 2 + 3 + ... + 87 + 88 + 89

s = 89 + 88 + 87 + ... +3 + 2 + 1

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2s = 90 + 90 + 90 + ... + 90 + 90 + 90

there are 89 of 90s

2s = 89(90)

2s = 8010

s = 4005