Given that the number is C.
The number divided by 7 is C/7
Difference means we will subtract 9 from C/7.
Therefore, the equation will be:
C/7 - 9 = 2 (multiply all terms by 7 to get rid of the fraction)
C - 63 = 14
C = 14 + 63 = 77
X = pencils, y = pens
8x + 6y = 8.50
4x + 4y = 5.....multiply by -2
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8x + 6y = 8.50
-8x - 8y = -10 (result of multiplying by -2)
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-2y = - 1.50
y = -1.50 / -2
y = 0.75 <=== pens cost 0.75
4x + 4y = 5
4x + 4(0.75) = 5
4x + 3 = 5
4x = 5 - 3
4x = 2
x = 2/4
x = 0.50 <== pencils cost 0.50
Parallel slope = 2
This is because the original line has slope 2. Parallel lines have equal slopes.
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Perpendicular slope = -1/2
The original slope 2 or 2/1 turns into -1/2 after flipping the fraction and the sign. Note the original slope and perpendicular slope multiply to -1. This is true for any pair of perpendicular lines where neither line is vertical.
