Working systematically

problem
Symmetricality

Age

14 to 18

Challenge level

Five equations and five unknowns. Is there an easy way to find the unknown values?
problem
Scratch cards

Age

14 to 16

Challenge level

To win on a scratch card you have to uncover three numbers that add up to more than fifteen. What is the probability of winning a prize?
problem
Expenses

Age

14 to 16

Challenge level

What is the largest number which, when divided into these five numbers in turn, leaves the same remainder each time?
problem
Home city

Age

7 to 11

Challenge level

Use the clues to work out which cities Mohamed, Sheng, Tanya and Bharat live in.
problem
Tet-trouble

Age

14 to 16

Challenge level

Is it possible to have a tetrahedron whose six edges have lengths 10, 20, 30, 40, 50 and 60 units?
problem
Dozens

Age

7 to 14

Challenge level

Can you select the missing digit(s) to find the largest multiple?
problem
Two egg timers

Age

7 to 11

Challenge level

You have two egg timers. One takes 4 minutes exactly to empty and the other takes 7 minutes. What times in whole minutes can you measure and how?
problem
A child is full of ...

Age

7 to 11

Challenge level

My cousin was 24 years old on Friday April 5th in 1974. On what day of the week was she born?
problem
Compare areas

Age

14 to 16

Challenge level

Which has the greatest area, a circle or a square, inscribed in an isosceles right angle triangle?
problem
Number sandwiches

Age

7 to 14

Challenge level

Can you arrange the digits 1, 1, 2, 2, 3 and 3 to make a Number Sandwich?