How many 1/3 pieces can be made from 2 pizzas, we know it is 6 and it is arrived by dividing 2 by 1/3 or multiplying by its reciprocal 3/1.
Hence to find how many 3/10 pieces can be made from 12/15 pizza, we have to divide 12/15 by 3/10 or multiplying by its reciprocal 10/3, i.e.
12/15 times 10/3= 8/3 or 2 2/3
What does that mean? This means that while 2 three-tenths pieces can be made, 2/3of 3/10 i.e. <span>2/3×3/10=2/10=1/5</span> or one-fifth of pizza will be left out.
So the answer is 2 three-tenths pieces can be made, and one-fifth pizza will be left out.
This can be solved using a system of equations.

Subtract y from both sides.

Substitute:

Subtract 80 from both sides:

Divide both sides by 5:

Substitute.
First convert the equation in the form of <em>y= mx + </em><em>c</em>
The equation will be like = y = 6x-5
value of m = 6
The slope of perpendicular line will be = -1/m = -1/6
For 20% out of 100% it would be 1/5 as you need 5 20s for 100