Estimate how many haircuts a person in the UK has in their lifetime. Would you estimate that men have more than women. How would you find out?
Life expectancy in the UK is 81 years. but babies do not need haircuts. (80 years to 1 significant figure)
Estimate people have a haircut every 12 weeks or so which is 4 haircuts a year
So \(4×80=320\) haircuts.
Men have a slightly shorter life expectancy but may have haircuts more often, so it is not immediately clear whether men have more haircuts.
You could do surveys asking how often people have haircuts – try to get a representative sample of men and women of different ages etc. Or ask a sample of hairdressers and barbers how often their customers come to the shop.