(adsbygoogle = window.adsbygoogle || []).push({}); How Many??

Im trying to figure this question out from an old Final exam.

(a) In how many numbers with seven distinct digits do only the digits 1 to 9 inclusive appear (i.e. digit 0 is exluded)?

This one i got P(9,7) because there are 9 numbers and 7 ordered places to place 7 of the 9.

(b) How many of the numbers in (a) contain a 3 and a 6?

For this question i got C(7,5)*P(7,7). Don't know if this is correct....

(c) How many of the numbers in (a) contain neither a 3 nor a 6?

This one it's either

P(8,7) + P(8,7) - P(7,7)

or simply

P(7,7)

Im pretty sure i got (a) but for (b) and (c) i need some help. Am i close?

Thanks

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# How Many?

Can you offer guidance or do you also need help?

Draft saved
Draft deleted

**Physics Forums | Science Articles, Homework Help, Discussion**