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# Fast speed distance time in head watch

1. How would you calculate what speed you are travelling at if you cover 61 miles in 1hr and 5mins?

I have my OASC exam soon and need to be able to calculate this type of question in my head, quickly! What's the best way of going about it? Thanks!
2. (Original post by jacoballen66)
How would you calculate what speed you are travelling at if you cover 61 miles in 1hr and 5mins?

I have my OASC exam soon and need to be able to calculate this type of question in my head, quickly! What's the best way of going about it? Thanks!
Did you make that question up? You could approximate it in your head or work it out as a fraction (assuming by the way that you want the answer in mph)?

I doubt you would be given that as a mental arithmetic question. If you did make it up then we can come up with questions that are more likely to come up.
3. I tend to think about the units. So in this question you're being asked for the speed, which is measured in miles per hour, or miles/hour. That suggests that you should divide the number of miles by the number of hours.
4. (Original post by notnek)
Did you make that question up? You could approximate it in your head or work it out as a fraction (assuming by the way that you want the answer in mph)?

I doubt you would be given that as a mental arithmetic question. If you did make it up then we can come up with questions that are more likely to come up.
Thanks for your response, I got this question from 'RAF officer & aircrew' book by Richard McMunn. There are a few errors in this book so I'm already abit suspicious of the questions haha. Do you think a calculation such as the one stated would be asked if you weren't allowed a calculated or pen and paper in the exam?
5. This calculation seems a little bit involved for mental arithmetic, but it makes sense if it's asking for 'roughly what speed' - it's obviously a little bit less than 60mph but exactly how much isn't a mental arithmetic thing to my mind. The answer, of course, is 61/1.083333 (that being 1hr 5mins as a decimal) = 56mph.
6. (Original post by Reality Check)
This calculation seems a little bit involved for mental arithmetic, but it makes sense if it's asking for 'roughly what speed' - it's obviously a little bit less than 60mph but exactly how much isn't a mental arithmetic thing to my mind. The answer, of course, is 61/1.083333 (that being 1hr 5mins as a decimal) = 56mph.
Yeah that's what I thought! Seemed too involved to be done in head. Thanks for clearing that up though, as long as it's not me that's missing an obviously easy way to figure it out.
Thanks again chaps.
7. (Original post by jacoballen66)
Thanks for your response, I got this question from 'RAF officer & aircrew' book by Richard McMunn. There are a few errors in this book so I'm already abit suspicious of the questions haha. Do you think a calculation such as the one stated would be asked if you weren't allowed a calculated or pen and paper in the exam?
If it's the only one that doesn't have a whole number answer then I would guess that it's a mistake. I've done a few different interview tests before that have involved mental arithmetic speed/time questions and nothing like this would have been in them.
8. (Original post by jacoballen66)
How would you calculate what speed you are travelling at if you cover 61 miles in 1hr and 5mins?

I have my OASC exam soon and need to be able to calculate this type of question in my head, quickly! What's the best way of going about it? Thanks!
If I absolutely had to do this in head, I would do this, I would note that 5 minutes = 1/12 of an hour which is roughly 0.08 of an hour since 12x8=96. Then:

speed = distance/time =

mph

where I've used the binomial expansion. The correct value is 56.3 to 1 d.p. so that approximation is 0.1/56.3 x 100 = 0.2% out, roughly.

Or quicker and dirtier: 1/12 = 0.08 approx = 0.1 approx, then use the rule of thumb that to divide by 1.1 approximately, you subtract 1/10 the value e.g.

The approximation here is out by about 1.4/61 x 100 = 2.3% approx, which isn't too bad. This approximation follows from the binomial expansion too, of course.

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