Daily pupils of the eighth classes have 5 lessons 45 min. each, 3 changes for 10 min. and 1 change 20 min. What is the time have to carry out daily studying the eighth classes at school?

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5*45=225 min. time of lessons of 3*10+20=50 min. change of 225+50=275 min. at school 225:60=4 hours 35 minutes
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