Two sides of a triangle measure 5 in. and 12 in. Which could be the length of the third side?

For three lengths to form a triangle, the third side must be greater than the difference of the other two sides and less than their sum. Here, 12 − 5 = 7 and 12 + 5 = 17, so the third side must be between 7 and 17 inches. Of the choices, 10 inches fits.

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