Perimeter of a triangle with unknown sides

The lengths of the sides of a triangle are y, y + 1, and 7 centimeters.  If the perimeter is 56 centimeters,
what is the value of y?

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To find the perimeter of a triangle, simply add up the sides.

y + y + 1 + 7 = 56   {added given sides and set equal to given perimeter}
2y + 8 = 56   {combined like terms}
2y = 48   {subtracted 8 from each side}
y = 24   {divided each side by 2}

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