Question

walter is contracted to pour a concrete slab for the driveway of a new home. the water in concrete can freeze if the outdoor temperature is below 40°f. concrete needs about a week to set. the temperature for the next 7 days will be about 57°f plus or minus 18 degrees. which statement is true?
a) walter can pour the concrete because the temperature will always be above 40°f.
b) walter can pour the concrete because the average temperature will be above 40°f.
c) walter should wait to pour the concrete because the temperature may be as low as 41°f.
d) walter should wait to pour the concrete because the temperature may be as low as 39°f.

Explanation:

Step1: Analyze the temperature range

The temperature for the next 7 days will be about \( 57^\circ\text{F} \) plus or minus \( 18^\circ\text{F} \). So the minimum temperature in this range is \( 57 - 18 = 39^\circ\text{F} \), and the maximum is \( 57 + 18 = 75^\circ\text{F} \).

Step2: Evaluate each option

• Option A: Says temperature will always be above \( 40^\circ\text{F} \). But the minimum is \( 39^\circ\text{F} \), so this is false.
• Option B: Says average temperature will be above \( 40^\circ\text{F} \). The average is \( 57^\circ\text{F} \), which is above \( 40^\circ\text{F} \), but we need to check if the temperature can go below \( 40^\circ\text{F} \) (since concrete water freezes below \( 40^\circ\text{F} \)). The minimum is \( 39^\circ\text{F} \), so it can go below, so this is not sufficient to conclude he can pour.
• Option C: Says temperature may be as low as \( 41^\circ\text{F} \). But we calculated the minimum as \( 39^\circ\text{F} \), so this is false.
• Option D: Says temperature may be as low as \( 39^\circ\text{F} \). Since \( 39^\circ\text{F} < 40^\circ\text{F} \), the water in concrete can freeze. So Walter should wait because the temperature may be below \( 40^\circ\text{F} \) (as low as \( 39^\circ\text{F} \)).

Answer:

D) Walter should wait to pour the concrete because the temperature may be as low as \( 39^\circ\text{F} \).