Associated Topics || Dr. Math Home || Search Dr. Math

```
Date: 04/26/99 at 17:09:26
From: Tracy Schneekloth
Subject: Spacecraft

A spacecraft is launched at 7:45 a.m. on Monday. It is in flight for 5
days 3 hours and 18 minutes. What time does the spacecraft land?

I don't understand it at all!
```

```
Date: 04/26/99 at 19:18:13
From: Doctor Teeple
Subject: Re: Spacecraft

Hi Tracy,

Thanks for writing Dr. Math.

Let's start from the beginning and see if we can help you understand
this question a bit more. I'll do a similar one all the way through to
give you an example.

First, what is the question asking? Well, it says the spacecraft is
in space for a certain amount of time and then lands. So we need to
add all of the time that the spacecraft is in space.

Let's suppose that the spacecraft was in space for 4 days, 3 hours,
and 22 minutes. (Remember, we're just doing a similar question
here). For me, the best way to add time is to do it in parts. That
means we'll add the minutes, hours, and days separately.

So we start with 7:45 am on Monday. What if the spacecraft was in the
air for 22 minutes total? What's 22 minutes after 7:45 am? We can
write it this way:

7:45 a.m.
+   22 minutes
------

7:45 a.m.
+   22 minutes
------
7:67 a.m.

Uh oh, something's wrong here, since there is no 7:67 a.m. We need to
take into account that there are only 60 minutes in an hour. So we
carry the 60 minutes and make it into 1 hour. Do you see how this now
becomes 8:07 a.m.?

Now we need to add on the hours. We get:

8:07 a.m.
+ 3    hours
------
11:07 a.m.

That one's straightforward. Normally when you add hours, you need to
watch out for when the answer is bigger than 12. If it is, then either
you've gone from a.m. to p.m. on the same day, or you've gone from
p.m. to a.m. on the next day and you need to add another day.

Now we need to add on the days. Since we're adding 4 days, we just
count 4 days after Monday, which is:

Monday    Tuesday    Wednesday    Thursday    Friday
=========> 1 day ===> 2 days ====> 3 days ==> 4 days

Friday. So the spacecraft lands at 11:07 a.m. on Friday.

So if it becomes overwhelming to add time and days, separate them and
do them in parts. If you need more help with time, here is a page from
the Dr. Math archives:

Adding and Subtracting Units of Time
http://mathforum.org/dr.math/problems/shellie12.11.98.html

Also, please feel free to write back if you have more questions or

- Doctor Teeple, The Math Forum
http://mathforum.org/dr.math/
```
Associated Topics:
Elementary Calendars/Dates/Time
Middle School Calendars/Dates/Time

Search the Dr. Math Library:

 Find items containing (put spaces between keywords):   Click only once for faster results: [ Choose "whole words" when searching for a word like age.] all keywords, in any order at least one, that exact phrase parts of words whole words

Submit your own question to Dr. Math
Math Forum Home || Math Library || Quick Reference || Math Forum Search