The maths problem

On Monday, The Times reported that 46% of teachers in a national evaluation were unable to work out the answer to 10 x 2 + (6 - 4) ÷ 2.

Neither could I, nor many of my colleagues.

We were determined to prove the answer is 11.

Our research led us to an article, "If Maths is Universal, Why can't it Answer a Stupid Facebook Problem?", in which the author, Tara Haelle, discusses a maths problem that has gone viral: 6 ÷ 2 (1+ 2). Is the answer 1 or 9?

If you're following the Bodmas convention of maths, as we do in South Africa, then 9 is correct and 1 is incorrect. But if you understand the obelus, or ÷ symbol, as "dividing everything to the left of it by everything to the right of it", your answer would have been 1.

What is the answer to 10 x 2 + (6 - 4) ÷ 2? Is it 11 or 21?

Nick Taylor, who conducted the evaluation, says that since my colleagues and I haven't been at school for a while, we've forgotten the Bodmas convention and are working from left to right to arrive at 11.

Bodmas, he says, is based on logic. If you buy 2 hamburgers at R3 each and 4 cold drinks at R2 each, you would first do the multiplication, then the addition.

Solving maths problems involves applying a set of conventions. The bottom line, says Haelle, is that "order of operations conventions such as Bodmas are not universal truths in the same way the sum of 2 and 2 is always 4. Conventions evolve throughout history in response to cultural and technological shifts."

The current convention, like all conventions, is somewhat, but not completely, arbitrary.

After a day of debate, we had to concede that there is an unambiguous answer to the problem - 21.