Question

Solve each problem by forming a pair of simultaneous equations:

Find two numbers with a sum of 15 and a difference of 4.​

Answer 1

11/2 and 19/2

Explanation:

We have to make a system of equations:

1) X + Y = 15

2) X - Y = 4

Working on the first one:

X = 15 - Y

And now let's plug it in the second one:

(15 - Y) - Y = 4

15 - 2Y = 4

2Y = 11

Y = 11/2

Let's substitute this in one of the two equations:

X + 11/2 = 15

X = 19/2

Answer 2

5.5, 9.5

Explanation:

Let x and y be the numbers

x+y = 15

x-y = 4

Add the two equations together to eliminate y

x+y = 15

x-y = 4

------------------

2x = 19

Divide by 2

2x/2 =19/2

x = 9.5

Now find y

x+y = 15

9.5+y = 15

Subtract 9.5

x = 15-9.5

x =5.5