13. You are correct. You multiply the outer 5 with each term inside, and add.
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14. The number 0 goes in the first blank and 8 goes in the second blank. So we have 8+0 = 8. The identity property of addition says that adding 0 to any number leads to the same result. In terms of algebra, x+0 = x.
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15. The fraction 1/8 goes in the first blank and 1 goes in the second blank. We have the equation 8(1/8) = 1. Multiplying any nonnegative number x with its reciprocal 1/x leads to 1.
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16. The number 1 goes in the first blank and -4 goes in the next blank. This property is similar to the property mentioned in problem 14. This time we're working with the multiplicative version. We have the equation -4*(1) = -4
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17. The letter a goes in the first blank and x+3 goes in the second blank. So the last equation is a = x+3. The transitive property is the idea of us chaining equations together. It's like saying "if A goes to B, and B goes to C, then A goes to C". Think of it like taking a shortcut bypassing B entirely.