The temperature 38

The temperature has been dropping 2 degrees every hour, and the temperature at 10:00 AM was -15 degrees Fahrenheit. At what time was the temperature 0 degrees Fahrenheit?

Result

t₀ = 2:30 hh:mm

Step-by-step explanation:

$$\begin{gathered} T=a\cdot t+b \\ a=-2\text{°F/h} \\ -15=a\cdot 10.00+b \\ -15=(-2)\cdot 10.00+b \\ b=5 \\ b=\frac{5}{1}=5 \\ b=5 \\ T(t)=-2\cdot t+5 \\ T(t_0)=0\text{°F} \\ 0=a\cdot t_0+b \\ 0=(-2)\cdot t_0+5 \\ 2t_0=5 \\ {t}_0=\frac{5}{2}=2.5 \\ {t}_0=\frac{5}{2}=2.5=2:30\text{hh}:\text{mm} \end{gathered}$$

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