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Progress Test 2, Qu 8

• Topic Author

Madox01 created the topic: Progress Test 2, Qu 8

I totally understand the answer given in the back of the book...however silly me didnt realise that there was 15degs separation in the longitude, i worked it out using the conversions, anyway the answer i get is different...i just cant seem to pinpoint where this error occured, obviously its there just cant see it

BOD A 0500LMT, E 131, E 131 is 8hrs 44

? 05 00
- ? 08 44

i got ?2016UTC

BOD B 1830LMT, E 146, E 146 is 9hrs 44 (i can see the 1hour difference in the longitudes)

? 18 30
- ? 9 44

i got ?0846UTC

Which brings me to my answer

? 20 16
- ? 08 46

Which gives me the 11hrs 30minutes...

Can anyone work out what ive done wrong, for about the 5th time i still cant see it

• Posts: 1169

Richard replied the topic: Re: Progress Test 2, Qu 8

This is a common mistake that can be made when dealing with time calculations. When you subtracted 0846 from 2016 you actually took the EOD at B from the BOD at A - completely opposite to what you should do.

Daylight available = EOD - BOD

The easiest way to avoid an error like that is to replace your "?" marks with some date e.g. the 10th. The problem then becomes:
```BOD A 0500 LMT, E131 = 8:44 ahead of UTC

10 05 00
-    08 44
========
09 20 16  i.e. 20:16 on the 9th day. It's the day before!

EOD B 1830 LMT, E146 = 09:44 ahead of UTC

10 18 30
-    09 44
========
10 08 46 i.e. 08:46 on the 10th.

The difference between BOD and EOD is EOD - BOD:

10 08 46
- 09 20 16
========
00 12 30

The daylight available is 12 hrs 20 minutes, option (d)```
As I said, you were tricked into taking the apparently earlier time (08:46) away from the apparently later time (20:16) to get the answer of 11:30.

However they were on different days and you would have spotted your mistake more easily if you had used some date value instead of the "?" to help keep track of day changes.

You're not the first to get tricked out that way so don't worry

Cheers,

Rich

• Topic Author

Madox01 replied the topic: Re: Progress Test 2, Qu 8

Hi Rich,

i knew it was something really silly, having question marks there instead of fake dates really did complicate the working out

No doubt i will have something else that doesnt make sense so im thanking you in advance for the future time your needed

Cheers!