Question

NASA uses a launch clock to measure time before and after lift-off. It takes 2 hours and 15 minutes of preparations on base, 20 minutes to travel to the launch pad, and 40 minutes of pre-launch checks once in the spacecraft. When should the astronauts begin preparation?
–3 hours 15 minutes, because all the preparation times add to 3 hours and 15 minutes
–3 hours 35 minutes, because all the preparation times add to 3 hours and 35 minutes
–2 hours 35 minutes, because all the preparation times add to 2 hours and 35 minutes
–2 hours 15 minutes, because all the preparation times add to 2 hours and 15 minutes

Answer 1

To determine when the astronauts should begin preparations, we need to add up all the times required before the launch:

1. Preparation on base: **2 hours and 15 minutes**
2. Travel to the launch pad: **20 minutes**
3. Pre-launch checks in the spacecraft: **40 minutes**

Now let's convert all times to minutes for easier addition:

- 2 hours and 15 minutes = \(2 \times 60 + 15 = 120 + 15 = 135\) minutes
- 20 minutes = 20 minutes
- 40 minutes = 40 minutes

Now we add these times together:

\[
135 + 20 + 40 = 195 \text{ minutes}
\]

Next, we convert 195 minutes back to hours and minutes:

- 195 minutes = \(3 \text{ hours} + 15 \text{ minutes}\)

Since the total time before launch is 3 hours and 15 minutes, the astronauts should start their preparations 3 hours and 15 minutes before the scheduled lift-off time.

Therefore, the correct answer is: **–3 hours 15 minutes, because all the preparation times add to 3 hours and 15 minutes.**