Answer:
40%
Step-by-step explanation:
12 ÷ 20 = .6
You can convert the .6 to a percentage by multiplying it:
.6 x 100 = 60%
If 12 is 60% of 20, then that means 40% was taken away.

Hope you could get an idea from here.
Doubt clarification- use comment section.
15 & 16 & 17
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C. It is the mean. Add all of the ages up and divide by how many there are.
The -1 means that y = -1, so point is one unit below the x-axis. In (5, -1), the x is positive, which could put the point in either the first quadrant or the fourth. With the y being negative, however, it means that the point is in the fourth quadrant. Those are your 2 true statements.