How many two-digit positive integers can be formed the digits 1,5,6, and 8 if no digit is repeated?

12

Step-by-step explanation:

There are 4 different digits to choose from. Since we want 2-digit number, we will see what digits can we put in place of 1st digit and what digit can we place in place of 2nd digit.

Hence, how many digits (from 1,5,6 and 8) can be placed in the 1st digit of the number we want?

Any one of the four digits (1,5,6, or 8).

Now, How many digits (from 1,5,6 and 8) can be placed as the 2nd digit of the number we want?

Any one of the THREE digits (since repetition is not allowed, we disregard the initial digit).

Thus the number of two-digit positive integers is 4 * 3 = 12