Outside a home, there is a 4-key keypad with letters Upper A comma Upper B comma Upper C comma and Upper D that can be used to open the garage if the correct four-letter code is entered. Each key may be used only once. How many codes are possible?

24 possible codes

Step-by-step explanation:

If every letter may be used only once, we can calculated how many codes are possible using the rule of multiplication as:

__4 * ___3 *  2 * ___1 = 24

1st letter     2nd letter      3rd letter       4th letter

Because for the 1st letter of the code, we have 4 options, letter A, B, C and D.

Then for the 2nd letter, we only have 3 options because we can not choose the letter that we choose in the 1st letter.

So, the 3rd letter just have 2 options and finally, there is just one option for the 4th letter.

168

step-by-step explanation:

i am pretty sure that the answer is 168