Answer:
A. Selection Bias
Step-by-step explanation:
Selection bias is the bias introduced by the selection of individuals, groups, or data for analysis in such a way that proper randomization is not achieved, thereby ensuring that the sample obtained is not representative of the population intended to be analyzed. This is represented by choosing the students without glasses.
Think of the letter 'a' to represent 1 apple.
a = 1a = 1 apple
2a = 2 apples
3a = 3 apples
and so on
Adding 7a with 4a means we have 7 apples and we add on 4 more. We'll have 7+4 = 11 apples total.
Algebraically we write 7a+4a = 11a to do this using shorthand.
The 9-7 portion is calculated like you'd expect and it simplifies to 2.
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Here's what the step by step picture looks like
(7a+9) + (4a-7)
7a + 9 + 4a - 7
(7a+4a) + (9-7)
11a + 2
I think it eould be 17 feet. 5 plus 8 plus 4 is 17.