Mastering Rounding: Understanding 4 Digits in Math Exams

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I'm doing a past exam paper and there's a question telling me to round to 4 digits. Does this mean rounding to 4 significant figures, 4 decimal places, or something else? Or is it ambiguous? (I really hope it isn't this one)
 

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I would have said 4 sig figures but it is poorly worded
 
Gwilim said:
I'm doing a past exam paper and there's a question telling me to round to 4 digits. Does this mean rounding to 4 significant figures, 4 decimal places, or something else? Or is it ambiguous? (I really hope it isn't this one)

mg_phys is correct, unless the topic of the question demands the other interpretation. The specification for rounding "... to 4 digits" does not say anything about which direction or place value in relation to the decimal point; so the wording must mean "4 significant figures".
 
In the context of the module we are dealing with word lengths. So, in a fixed point number, zeros after the decimal point would count as digits? I think significant figures is probably the safest assumption when fixed point is not explicitly specified, unless someone tells me otherwise given this information.
 
Remember the zero BEFORE the decimal point is not significant
All these are 4 sig figures 1.234, 1.230, 0.1234, 0.1230
 
Right, but 0.01234 is 4 significant figures, and 0.0123 is the same as a fixed point number rounded to 4 digits?
 
Gwilim said:
Right, but 0.01234 is 4 significant figures,
Yes, think of it as 1.234 x10^-2

and 0.0123 is the same as a fixed point number rounded to 4 digits?
0.0123 is three sig figs = 1.23 x10^-2
 
mgb_phys said:
0.0123 is three sig figs = 1.23 x10^-2

This is where I'm unsure.. 1.23x10^-2 is a floating point number. Do I just assume a number has a floating point unless I'm told it's fixed, even when it's presented as a fixed point? This has to do with how numbers are stored on a computer rather than rounding off measurements.

I suppose my guess is as good as anybodys.
 
Storing floating point number sin a computer is a little different.
They are stored in exponent notation ( 0.1234 E-2 )
But the fraction par tis of course stored as binary - so it is really the sum of 1/2 + 1/4 + 1/8 + 1/16 + 1/32 and so. Then there is an exponent stored as a regular binary number.
This gives some odd results, numbers which fit into the powers of 2 can be stored exactly while other simple fractions like 1/10 can only be approximated.

If you are interested the normal way of storing floats is called IEEE 754