Final answer:
To represent the part of Kristy's button collection that is red as a decimal, divide the number of red buttons by the total number of buttons.
Step-by-step explanation:
To find the decimal that represents the part of her button collection that is red, we need to divide the number of red buttons by the total number of buttons. In this case, Kristy has 24 red buttons out of a total of 100 buttons. So, the decimal that represents the part of her collection that is red is 0.24.