Sum and difference of two numbers

The sum of two numbers is 2. They have a difference of -16. What are the 2 numbers??

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x = one number
y = other number

x + y = 2   {the sum of two numbers is 2}
x - y = -16   {they have a difference of -16}
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2x = -14   {added the two equations}
x = -7   {divided by 2}

x - y = -16   {second equation}
-7 - y = -16   {substituted -7, in for x, into second equation}
+7         +7
-y = -9   {added 7 to each side}
y = 9   {divided each side by -1}

one number is -7
other number is 9

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