How many four-digit numbers can be formed from the digits 1 and 2 if repetitions are allowed?
And what is the best way of working it out, other than just listing all the possibilities?
Thanks!
And what is the best way of working it out, other than just listing all the possibilities?
Thanks!
Dragon.Jade
Favorite Answer
Hello,
First digit is either 1 or 2, hence you have two possibilities...
Second digit is either 1 or 2, hence you have again two possibilities...
Third digit is either 1 or 2, hence you have yet again two possibilities...
Last digit is either 1 or 2, hence you have guess what? Two possibilities...
So the total number of all possibilities is:
2 × 2 × 2 × 2 = 16 possibilities.
No need to list them all.
Logically,
Dragon.Jade :-)
Muammar
in the required four digit number,
the ones place may be a 1 or a 2
----- possibilites = 2
the tens place may be a 1 or a 2
-----possibilities = 2 * 2
the hundreaths place may be a 1 or a 2
----- possibilities = 2 * 2 * 2
the thousandths place may be a 1 or a 2
-----possibilities = 2 * 2 * 2 * 2
= 16
Thus, there are 16 possibilities
Amber
16
Crazins
n is number of objects so n=2 and r is the number of choices so r=4 so n^r so 2^4=16. 16 possibilities.