The Sum of Two Numbers is 21 and Their Difference is 5

The sum of two numbers is 21 and their difference is 5. 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 21. In other words, x plus y equals 21 and can be written as equation A:

x + y = 21

The difference between x and y is 5. In other words, x minus y equals 5 and can be written as equation B:

x - y = 5

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

x - y = 5
x = 5 + y

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

x + y = 21
5 + y + y = 21
5 + 2y = 21
2y = 16
y = 8

Now we know y is 8. Which means that we can substitute y for 8 in equation A and solve for x:

x + y = 21
x + 8 = 21
X = 13

Summary: The sum of two numbers is 21 and their difference is 5. What are the two numbers? Answer: 13 and 8 as proven here:

Sum: 13 + 8 = 21
Difference: 13 - 8 = 5

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