Question

15 POINTSSSSSS!!!

The sum of three numbers is 15
The second number is 2 times the first.
The third number is 20 less than the second.
What is the third number?

Answer 1

a + b + c = 15

a + 2xb

2xb + -20c

For the first number, it is 7

For the second number, it is 14

For the third number, it is -6

MATH CHECK:

14 - 20 = (-6)

14 + (-6) = 8

8 + 7 = 15

THIRD NUMBER = (-6)

Answer 2

x+y+z=15

y =2x

z=y-20

substitute these equations into the first

x+2x+y-20 =15

now substitute 2x in for y

x + 2x +2x-20 =15

combine like terms

5x-20 =15

add 20 to each side

5x = 35

divide by 5

x=7

y =2x

y =14

z = y-20

z=14-20

z=-6

The third number is -6