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'Put Out the Flags' printed from http://nrich.maths.org/

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Why do this problem?

This problem gives practice in calculating with percentages. It can be approached by trial and improvement but the equivalence between fractions and percentages is very useful.

Key questions

What fraction is $50$%? and $35$%?
What would be a sensible number to try first?
Do you think they will not have a whole number of flags?
Tim could have $100$ flags but could he have less than $100$ flags?
If $50$% of Tim's flags are blue, what does this tell you about the number of flags Tim must have?
As $35$% of Tim'??s flags are red, what does this tell you about the number of flags Tim must have?

Possible extension

Learners could devise and solve a second part to the question, similar to that one in the problem.

Possible support

Suggest working with counters or drawing the flags starting with a suitable arbitrary number and working by trial and improvement.