/sci/ - Science & Math

Lol'd at the pic

upgrade your brain cells. it is not hard but doing it in this century?

9^3 - 1

That pic just reminded me of something I saw in the T-Mobile store last night... I should have taken a photo of it.

Every single phone had a little sign that said:

$199
or
$199 down payment + $10/month for 24 months

The amount was different for each phone, but every single one of them said $X or $X + $Y/month for Z months.

>>3850635
How?

1 digit numbers: 9 different choices
2-digit numbers: 9 choices for first digit, 9 for second...

see where this is going?

Start by finding all the numbers which do contain 7.

Remember to count the numbers which contain 7, and not the individual 7s.

Concept behind the problem is simple.

>>3850605
lol @ pic
>planet fitness
Oh that makes sense.

>>3850605

>2011
>acting on this marketing bull shit thinking you get a better deal
>mfw

10x18=180
199/18= approximately 11$ per month

You write a program that does it for you.

> answer isn't hard
> 728
729. There are 728 3-digit numbers that don't contain a '7'. But you forgot about 1000.

Of all the numbers except 1000 (1000 total), 10% have a 7 as their first digit (if you write zeroes whenever there are less digits). So subtract 10% to get to 900.
Of all the numbers that don't start with a 7, 10% will have a 7 as the second digit. So subtract 10% again to get to 810.
Of all the numbers that remain, 10% will have a 7 as their last digit. Subtract 10% of 810 to get to 729.
Add 1 because 1000 wasn't included yet and you'll have 730.

Not sure how you got to 728.. forgot 0 and 1000?

>>3850890
This is right, though the method is weird. I fucked up.

Removing one symbol from our base-10 symbols gives us base 9. So how many base-9 numbers are there in 3 positions? 9^3 = 729. Plus 1000 is 730.

So, just some blackup there. I feel embarrassed about my 729 answer.

>>3850911
Different anon here. 729 is right. 0 is not a positive integer, OP wants positive integers.

>>3851036
ooh, nice catch