Question 20
KenKen is a number puzzle. Fill this $4×4$ grid with 1, 2, 3 and 4 so that each row and each column contains each number once. Thick lines divide it into cages. Each cage label gives an operation and its result. For example, $7+$ means the cage numbers sum to 7; $2-$ means the difference between its two numbers is 2; $2÷$ means the larger divided by the smaller is 2; and $4×$ means the product is 4. What number belongs in the starred cell?
