x = number of 1-cent stamps
y = number of 8-cent stamps
z = number of 12-cent stamps
We have 31 stamps all together, so x+y+z = 31.
"I have 4 more 1-cent stamps than 8-cent stamps" means we have the equation x = y+8. Whatever y is, add 8 to it to get x. Solve for y to get y = x-8.
You also have "twice as many one cent stamps as 12 cent stamps", so x = 2z. Solving for z gets you z = 0.5x
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x+y+z = 31
x+x-8+z = 31 ... y replaced with x-8
x+x-8+0.5x = 31 ... plug in z = 0.5x
2.5x-8 = 31
2.5x = 31+8
2.5x = 39
x = 39/2.5
x = 15.6
Your teacher made a typo somewhere because we should get a positive whole number result for x (since x is a count of how many 1-cent stamps we have).
There’s no picture, please post one
With the equation:
0.15 x = 30
x = 30 : 0.15 = $200
A regular price of TV is $200.
Which could not be used to determine x ( we shall plug in the value 200 ):
A ) 0.15 * 200 = 200 - 30
30 ≠ 170
B ) 0.85 * 200 = 200 - 30
170 = 170 ( correct )
C ) 200 - 0.15 * 200 = 200 - 30
200 - 30 = 200 - 30
170 = 170 ( correct )
D ) 0.15 * 200 = 30
30 = 30 ( correct )
Answer:
A ) 0.15 x = x - 30
