Morning

Jana rose in the morning in the quarter to seven. She slept nine and a half hours. When did she go to sleep?

Result

t = 21:15 hh:mm

Step-by-step explanation:

$$\begin{gathered} t_1=6+3\mathrm{/}4={\displaystyle \frac{27}{4}}=6.75\text{ h } \\ {t}_2=9+1\mathrm{/}2={\displaystyle \frac{19}{2}}=9.5\text{ h } \\ {t}_3=t_1-t_2=6.75-9.5=-{\displaystyle \frac{11}{4}}=-2.75 \\ t=t_3+24=(-2.75)+24={\displaystyle \frac{85}{4}}=21.25=21:15\text{ hh}:\text{mm} \end{gathered}$$

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