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.

If you divide the larger number by the smaller number when both are in equal units, the number you get is the 'x' you are looking for.

Great, thanks for your help, i wasn't converting the methane to ppm from ppb which is where i was going wrong.

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

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