Math CentralQuandaries & Queries


Question from Mark, a student:

How many 3 digit positive integers are odd and do not contain the digit 5?

Hi Mark,

Since it is a three digit number the hundredths digit can't be 0 and you also don't want it to be 5 so that just leaves 8 choices for the hundredths digit. The tens digit can't be 5 so the number of choices for the tens digit is 9. Thus there are 8 × 9 = 72 possible choices for the first two digits. Since the 3 digit number os odd its units digit must be odd. But it can't be 5 so how many choices are there for the units digit? How many possible choices for the 3 digit number?


About Math Central


Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences.
Quandaries & Queries page Home page University of Regina PIMS