Note that questions like this don’t appear on the SAT, but they might appear on a SAT Subject Test.
For the first digit, you have four choices: 2, 3, 4, or 5.
Once you choose that first digit, you have three choices for the second digit.
Once you’ve chosen the first and second digits, you only have two choices for the third digit.
By the final digit, you actually only have one choice, because only one digit is left–you’ve already used up the other three.
What you want to do here is multiply these choices to figure out the total number of possibilities.
It takes a minute, but you can also get this just by listing the numbers. Start by listing the lowest one you can (2345) and go in order until you get to the highest one (5432). The ones that begin with 2 look like this:
2345, 2354, 2435, 2453, 2534, 2543
Then you list the ones that begin with 3:
3245, 3254, 3425, 3452, 3524, 3542
And so on:
4235, 4253, 4325, 4352, 4523, 4532
5234, 5243, 5324, 5342, 5423, 5432
Sure enough, 24 possibilities.
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