11 Plus Exams Forum

I am sure this is too easy, I make the answer 10 days but I feel its a trick question.

Here's the question


My friend George is really good at maths so I decide to ask him some tricky questions to see if I can catch him out. Needless to say he got it right.

Question

The area of mould growing on my bathroom wall doubles every day. After 13 days the area covered is 2880cm2. After how many days did the area first exceed 300cm2?

Yes easy just work backwards, halving.

After 13 days the area covered is 2880cm2. After how many days did the area first exceed 300cm2?

So 12 days was .... 1440 cm^2.

11 days was 720 cm^2

10 days was 360 cm^2 so 9 days isn't over 300

Could you please post questions only once in future?

Apologies - last minute panic! Thanks for your reply. I thought it was supposed to be a trick question, looked TOO easy.

It's a 'inverse operation' question - ie working backwards. I bet a lot of children panicked and got it wrong.