Question

Liam is making barbecue ribs over a fire. The internal temperature of the ribs when he starts cooking is 40°F. During each hour of cooking, the internal temperature will increase by 25%. The ribs are safe to eat when they reach 165°F.
Use the drop-down menus to complete an inequality that can be solved to find how much time, t, it will take for the internal temperature to reach at least 165°F.

Answer 1

Answer: You need to wait at least 6.4 hours to eat the ribs.

t ≥ 6.4 hours.

Step-by-step explanation:

The initial temperature is 40°F, and it increases by 25% each hour.

This means that during hour 0 the temperature is 40° F

after the first hour, at h = 1h we have an increase of 25%, this means that the new temperature is:

T = 40° F + 0.25*40° F = 1.25*40° F

after another hour we have another increase of 25%, the temperature now is:

T = (1.25*40° F) + 0.25*(1.25*40° F) = (40° F)*(1.25)^2

Now, we can model the temperature at the hour h as:

T(h) = (40°f)*1.25^h

now we want to find the number of hours needed to get the temperature equal to 165°F. which is the minimum temperature that the ribs need to reach in order to be safe to eaten.

So we have:

(40°f)*1.25^h = 165° F

1.25^h = 165/40 = 4.125

h = ln(4.125)/ln(1.25)  = 6.4 hours.

then the inequality is:

t ≥ 6.4 hours.