# 2010 Section 1 Question 5

5) D

Number of batches = 72 / 12 = 6 batches

40 minutes to prepare 1st batch
25 minutes in the oven (this time is used to prepare the 2nd batch).
5 minutes to cool.
Total time taken for 1st batch = 40 + 25 + 5 = 70 minutes
Since we started at 1 pm, the first batch will be ready by 2:10.
We can start preparing the second batch as soon as we put the first one in the oven, i.e. 40 minutes after 1 pm, i.e. at 1:40.
The second batch will take 40 minutes to prepare. Preparation finishes at: 1:40 + 0:40 = 2:20
Since the first batch was made at 2:10, and 5 mins were required to cool the first batch, only 15 minutes extra were inquired to prepare the second batch.
Baking time = 25 minutes
Cooling time = 5 mins
Total time for second batch = 25 + 15 + 5 = 45 mins.

All of the following batches will require 45 mins as well.

Total time needed to make 6 batches = 70 + 5(45) = 70 + 225 = 295 minutes

295 minutes = 4 hours 55 minutes

Since we started at 1 pm, we will finish at 5:55 pm