Postman quick question

1. Jun 17, 2012

synkk

Apostman delivers to in a street of houses numbered
from 1 to 1000, given that he refuses to deliver to houses with the digit 9 in the number, how many houses does he deliver to?

My working: From 0-100 he doesn't deliver to 10 houses, from 100-200 he doesn't deliver to 19 houses, 200-300 he doesnt deliver to 19 houses, 300-400 he doesnt deliver to 19 houses, from 400-500 he doesnt deliver to 19 house, from 500-600 he doesnt deliver to 19 houses, from 600-700 he doesnt deliver to 19 houses, from 700-800 he doesnt deliver to 19 houses, from 800-899 he doesnt deliver to 19 houses, from 900-100 he doesnt deliver to 99 houses.

adding them up you get 261 so 1000 - 261 you get 739. Is this correct? My friend told me it is 9^3 i.e 729, but i have no idea how he done that, could anyone explain?

2. Jun 17, 2012

SammyS

Staff Emeritus
Why 729?

How many three digit numbers are there using only the nine digits, 0 through 8 ?

3. Jun 17, 2012

skiller

Are you sure?
Correct.
Are you sure? (Even allowing for the fact that you made a typo with writing "900-100" instead of "900-1000".)