Application of simultaneous linear equations

Question

One number is 9 less than three times a second number. If the first number plus twice the second number is 16, find the 2 number

Answer 1

Hi Kimngi,

Let's use the variable, x , to represent the first number and the variable, y , represent the second number.

Since "one number is 9 less than three times a second number", we can write: x = 3y - 9

Also, using the text, "first number plus twice the second number is 16", we can write: x + 2y = 16

Now we can substitute the expression for x into the second equation and solve for y:

x + 2y = 16

3y - 9 + 2y = 16

5y - 9 = 16

5y - 9 + 9 = 16 + 9

5y = 25

y = 5

The second number or y is 5.

NOTE: The first number ,x, will be 3 • 5 - 9 = 15 - 9 = 6

The first number or x will be 6.