Noob ratio maths help

Soldato
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Looking for a little assistance with a maths questions for someone that hasn't studied in 18 years -

Taking two figures (380 ppm carbon dioxide and 1750 ppb methane), express the ratio of co2 to ch4 in the format x: 1, where x is a whole number given to two significant figures.

If someone could point me in the right direction it would be greatly appreciated.
 
Soldato
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1750 ppb = 1.75 ppm

So 380/1.75 = 217.14

So i guess the answer is 217.14 : 1

Except it asks for a whole number to 2 significant figures, not 2 decimal places - which wouldn't be a whole number anyway.

So the answer would be 220 : 1

But well spotted on the ppb I hadn't noticed that :p
 
Soldato
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Doesn't 'significant figures' mean 'integer', not nearest factor of 10? I made the answer 217:1

No, significant figures means just that, the first set of numbers starting with one that is not zero, then you round up as normal.

So 655,464 to 3 significant figures would be 655,000
to 2 significant figures would be 660,000
and to 1 significant figure would be 700,000
 
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