An office opens at 9 a.m. and closes at 5.30 p.m. with a lunch break of 30 minutes. What is the ratio of lunch break to the total period in the office?
Lunch break period = 30 minutes
9 a.m. to 5.30 p.m. is 7 hours and 30 minutes
1 hour is 60 minutes
⇒ 7 hours = 7 × 60 = 540 minutes
Total period in office = 540 + 30 = 570 minutes
Therefore, ratio of lunch break to the total period in the office = 
⇒ ratio = 
= 
Dividing numerator and denominator by 3 we get
⇒ ratio = 
Therefore, ratio of lunch break to the total period in the office is 1:18
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