A blog about teaching and learning in a maths classroom.

Monday, 11 July 2011 | 0 Comments

I got this flyer in the mailbox today (extract)...

The answer to the first question “CO2 is not even 1%! As a decimal it is 0.04%” immediately got me wondering, why say “as a decimal?” It’s just poor use of terminology, but I had a look at the rest of the numbers.

**Answer 1.**

My purpose here is not to question the data, although Answer 1 seems correct. Wikipedia agrees “[Carbon dioxide] is a gas at standard temperature and pressure and exists in Earth’s atmosphere in this state, as a trace gas at a concentration of 0.039% by volume.” So, CATA have rounded up.

**Answer 2.**

3% of 0.04% = 0.0012%. CATA have rounded down to 0.001%.

**Answer 3.**

2% of 0.001% = 0.00002%

(If the 0.0012% figure had been used, that would be 0.000024%)

CATA have it as 0.00001%.

There is an error here.

*Ways you could use this in class.*

1. Find the error shown above.

2. Has this organisation represented the facts/numbers well?

(Get the students to Answers the question in mass rather than percentages.)

Answer 1. The mass figure from Wikipedia, “The total mass of atmospheric carbon dioxide is 3.16×10^{15} kg (about 3,000 gigatonnes)”.

Answer 2. 3% of 3.16×10^{15} kg = 9.48×10^{13} kg

Answer 3. 2% of 9.48×10^{13} kg = 1.896×10^{12} kg

That is, 1 896 000 000 000 kg. Wouldn’t have looked as good on the flyer.

A PDF version of part of the flyer.

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**Simon Job** — eleventh year of teaching maths in a public high school in Western Sydney, Australia.

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