Answer :
Final answer:
Mary wants to have a cake ready by 13 o'clock. Considering the preparation, baking and cooling times, she needs to start at 11:15.
Explanation:
The question asks to calculate the time Mary should start the preparations to have the cake ready by 13 o'clock. Here are the step-by-step calculations:
- Convert everything to the same time scale. In this case, we choose minutes because it's the smallest common unit. So, 1 hour becomes 60 minutes.
- Add up the time it takes for each step: 30 minutes (preparation) + 60 minutes (baking) + 15 minutes (cooling) = 105 minutes total time.
- Deduct this total from the desired ready time (13:00). Here, remember that 13 o'clock is equal to 1 PM which is 780 minutes (12 hours x 60 minutes/hr + 1 hr x 60 minutes/hr). Hence, 780 minutes (13:00) - 105 minutes = 675 minutes.
- Convert the result back to hours: 675 minutes / 60 = 11.25, which means that 11:15 (quarter past eleven) is the time Mary should start preparing.
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