Sig. figs. and ratios

sudzs

I've recently returned to learning and I'm struggling with a question and hope someone can give me a bit of guidance!

If you're asked to give a ratio as a whole number and to 2 sig figs, would this be the way to do it??

eg 32 : 1550

= 32/1550

= 0.020645

= 2 x 10^2



So is 2 x 10^2 the answer or should the answer be 1 : 2 x 10^2




Any advice appreciated!

Michael Collins

Your instructions seem odd! You are asked to give a ratio e.g.

32:1550

as a "whole number", which means the natural numbers (or integers) like 0, 1, 2 or 3 etc,

then you are asked to give it to two significant digits, which is kind of odd, in this case it would mean

32:1550 = 0.020645 etc

to 2 significant digits this is

0.021

since leading zeros are not considered "significant digits", and the 6 after the 0.020 above means the trucated decimal is closer to 0.021 than to 0.020.

But neither of these are whole numbers, the nearest "whole" number is 0, and to two significant digits this is

0.00

I suspect they did not really mean "whole numbers" but actually just wanted you to convert a ratio to a decimal form, in which case the answer is

0.021

or in scientific notation

[latex] 2.1\times 10^{-2} [/latex].

Note the -2 exponent!

sudzs

Michael Collins wrote: »

or in scientific notation

[latex] 2.1\times 10^{-2} [/latex].

Note the -2 exponent!

Thanks for the reply.

I was so busy trying to remember the ALT thingy for an exponent i forgot the minus!!

I did it as above in the end, and also put in the 1 : for the ratio bit.... explaining that it was the ratio between 2 types of molecules. Would that be right?

Michael Collins

There's no point in expressing it as a ratio again by putting in the 'one'.The whole point is you've converted it from a ratio (basically a fraction) to a decimal, if you insist on putting it as a ratio, it would go after the number, not before. That is

0.021:1

But you'd never do that. Ever!

sudzs

Michael Collins wrote: »

There's no point in expressing it as a ratio again by putting in the 'one'.The whole point is you've converted it from a ratio (basically a fraction) to a decimal, if you insist on putting it as a ratio, it would go after the number, not before. That is

0.021:1

But you'd never do that. Ever!

crap.... I think I got it backwards.... and I forgot the minus.

Michael Collins

sudzs wrote: »

crap.... I think I got it backwards.... and I forgot the minus.

We all make mistakes when learning something new. Not to worry. Learn and improve etc.