Upper and lower bounds question

Wolf8312

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Apr 16, 2019
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Kelly ran a 1500m race in 260 seconds
The time was measured to the nearest second and the distance to the nearest 10 metres. Calculate maximum and minimum possible values of her speed in m/s (metres per seconds)

The answer in the book comes to 5.80 (max bounds) and 5.74 (min bounds) M/S respectively.

But although I can get the answer for the first maximum bounds, (1505 divided by 260.5) if I use 1495 divided by 259.5, I don’t get the right answer. Also approached the question a number of diffrent ways, and can never get both answers right at the same time!

Anyone tell me what I am doing wrong? My mother told me I am not supposed to round the time to the nearest second, and just divide 1505 into 260, but this again doesen’t yield the correct answer for the lower bound question, and besides it states in the question that the time was measured to the ‘nearest second’.
Not sure what to think now! Will leave this here and skip the question, before it begins to drive me insane!
 

Harry_the_cat

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Mar 16, 2016
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To get the max, you need to divide the max length by the minimum time, ie 1505/259.5 Your answer for 1505/260.5 is not 5.80, it is 5.78.

To get the min, you need to divide the min length by the maximum time.
 

Wolf8312

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Apr 16, 2019
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Oh sorry I should have said, the answer in the book is 5.80 (both to 2 DP, it says next to the answer). So I thought 5.79961464 needed to rounded up to 5.8...

But thanks a lot the answer is right! Also makes sense now as I wasn’t thinking in terms of the maximum and minumum possible values of the speed itself. Thanks a lot for taking the time!
 
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