Lets have your thinking caps on for this one please.
Think of a number between 1 and 10; multiply by 2; then add 5; then multiply by 50; then, if you’ve already had a birthday this year add 1756 if not add 1755. From this total subtract your birthyear.
You should be left with a three figure number - the first figure is the number you first thought of and the remaining two equal your age.
