Jack had

Jack had 4 hours of school.

He spent 45 minutes in the library, 1/2 hour on a science lecture, and 25 minutes on a lunch break.

How much time is left for the school to get over? (Write the answer as a fraction.)

Final Answer:

x =  7/3 = 2 ¹⁄₃ h

Step-by-step explanation:

$$\begin{gathered} s=\frac{45}{60}+\frac{1}{2}+\frac{25}{60}=\frac{45}{60}+\frac{30}{60}+\frac{25}{60}=\frac{45+30+25}{60}=\frac{100}{60}=\frac{5}{3}\doteq 1.6667\text{h} \\ x=4-s=4-\frac{5}{3}=\frac{4\cdot 3}{3}-\frac{5}{3}=\frac{12}{3}-\frac{5}{3}=\frac{12-5}{3}=\frac{7}{3}=\frac{7}{3}\text{h}=2.3333\text{h} \end{gathered}$$

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