Answer:
(a). $20,000
(b). The estimate will be lower than the actual amount.
Step-by-step explanation:
We have been given that Michael saves $423 dollars a month for college.
(a). We know that 1 year equals 12 months.
4 years = 4*12 months = 48 months.

Since we are asked to find the estimated amount of money Michael will save in 4 years, so we will estimate both quantities as:



Therefore, Michael will save approximately $20,000 in 4 years.
(b).
The estimate will be lower than the actual amount as we rounded $423 down $23 to nearest hundred that is $400 and rounded 48 up 2 to nearest ten that is 40.
Therefore, the estimate will be lower than the actual amount.
Answer: Choice D
(a-e)/f
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Explanation:
Points D and B are at locations (e,f) and (a,0) respectively.
Find the slope of line DB to get
m = (y2-y1)/(x2-x1)
m = (0-f)/(a-e)
m = -f/(a-e)
This is the slope of line DB. We want the perpendicular slope to this line. So we'll flip the fraction to get -(a-e)/f and then flip the sign from negative to positive. That leads to the final answer (a-e)/f.
Another example would be an original slope of -2/5 has a perpendicular slope of 5/2. Notice how the two slopes -2/5 and 5/2 multiply to -1. This is true of any pair of perpendicular lines where neither line is vertical.
For this case we have the following expression:

We must find the value of the expression when:

Substituting we have:

Finally, the value of the expression is:

ANswer:

The quotient is -8. This being because when a negative number is in parentheses, the negative will be the opposite: Positive. And we know 48 divided by 6 is 8. So the answer is B.