The Sum of Two Numbers is 81 and Their Difference is 4

The sum of two numbers is 81 and their difference is 4. What are the two numbers? Let's start by calling the two numbers we are looking for x and y.

The sum of x and y is 81. In other words, x plus y equals 81 and can be written as equation A:

x + y = 81

The difference between x and y is 4. In other words, x minus y equals 4 and can be written as equation B:

x - y = 4

Now solve equation B for x to get the revised equation B:

x - y = 4
x = 4 + y

Then substitute x in equation A from the revised equation B and then solve for y:

x + y = 81
4 + y + y = 81
4 + 2y = 81
2y = 77
y = 38.5

Now we know y is 38.5. Which means that we can substitute y for 38.5 in equation A and solve for x:

x + y = 81
x + 38.5 = 81
X = 42.5

Summary: The sum of two numbers is 81 and their difference is 4. What are the two numbers? Answer: 42.5 and 38.5 as proven here:

Sum: 42.5 + 38.5 = 81
Difference: 42.5 - 38.5 = 4

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The Sum of Two Numbers is 81 and Their Difference is 5
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