One day, River writes down the numbers 1,2,3,...999

What is the sum of all the digits that River wrote down?

thanks and please help :)

lokiisnotdead May 3, 2020

#1**0 **

Using the formula \(\frac{1}{2}(n)(n+1)\), we substitute the \(n\) as \(999\) to get \(\boxed{499500}\).

HannibalBarca May 3, 2020

#2**0 **

This is an arithemtic series with d = 1

S = (n/2) Γ (2a + (nβ1)d)

S = sum = 999/2 (2 + 998(1))

= 499500

ElectricPavlov May 3, 2020

#5

#4**0 **

Just to clarify: the problem asks **the sum of all the digits **that he wrote down.

lokiisnotdead May 3, 2020

#6

#8**+1 **

thanks Guest! even though this isn't the answer, your explanation was the part I was stuck on! (I couldn't figure out how many 1s, 2s, 3s, etc. there were)

So the answer is 1+2+3...9 =45 *300 = 13500.\(\)

lokiisnotdead
May 3, 2020

#9**+1 **

Sorry, I did have both of them but didn't read the question correctly:

(189, 300, 300, 300, 300, 300, 300, 300, 300, 300) >>>Total Number = 2889

(0, 300, 600, 900, 1200, 1500, 1800, 2100, 2400, 2700)>>Total Sum = 13500

Guest May 3, 2020