Titus works at a hotel. Part of his job is to keep the complimentary pitcher of water at least half full and always with ice. When he starts his shift, the water level shows 8 gallons, or 128 cups of water. As the shift progresses, he records the level of the water every 10 minutes. After 2 hours, he uses a regression calculator to compute an equation for the decrease in water. His equation is W –0.414t + 129.549, where t is the number of minutes and W is the level of water. According to the equation, after about how many minutes would the water level be less than or equal to 64 cups?

Step-by-step explanation:

If we are looking for how long it will take the level to be less than or equal to 64 cups, we are solving an inequality as opposed to an equation. It would look like this:

-.414t + 129.549 ≤ 64  We subtract 129.549 from both sides to get

-.414t ≤ -65.549 and then divide by -.414. But because we are dividing by a negative number we need to change the way the inequality is pointing:

t ≥ 158.3 minutes which is about 2.6 hours

t ≥ 158.33, or rounded, t ≥ 160.

Explanation:

The equation we're given is

W = -0.414t + 129.549, which an be written as

-0.414t + 129.549 = W.

We are asked to find the amount of time it would take for the water level to be less than or equal to 64 cups.  Plugging this information in, we have:

-0.414t + 129.549 ≤ 64

To solve this, we first cancel 129.549 by subtracting from both sides:

-0.414t + 129.549 - 129.549 ≤ 64 - 129.549

-0.414t ≤ -65.549

Now divide both sides by -0.414:

-0.414t/-0.414 ≤ -65.549/-0.414

t ≥ 158.33

(When we multiply or divide both sides of an inequality by a negative number, we must flip the inequality symbol)

b.an increase in a causes b to decrease