Explain why the answer is a decimal when you multipy a whole number by a decimal

Because by doing so you are making it only part of what it was. Like multiplying by 1 makes it itself, so less than one makes it less than what it was yet not everytime will it be a decimal

Because when you multiply a whole number by a decimal, the decimal is a number that is more broken up and not whole. Only when you multiply a whole number by a whole number it will come out to a whole number. When you have a decimal, it is not entirely whole and it is representing part of a number, so the total will only be the part of the number.