**B. 4204.** *a*, *b*, *c*, *d* are four positive numbers. Five of the products *ab*, *ac*, *ad*, *bc*, *bd*, *cd* are known: they are 2, 3, 4, 5 and 6. What is the value of the sixth product?

(3 points)

**K. 217.** Three kinds of bombs can be placed on a squared playing field. When a bomb explodes, it will destroy its own cell and the cells around, including the contents of those cells. The *diagram* shows the ranges of the three types of bombs. (The numbers indicate the location and type of the bomb.) If a cell destroyed by a bomb contains another bomb, that bomb will also explode, together with all cells in its range. Place 2 of each kind of bomb on the squared field so that the largest possible number of cells are destroyed if any of the bombs is exploded.

(6 points)

This problem is for grade 9 students only.

**K. 219.** Five different positive integers were chosen and pairwise multiplied together. The results are as follows: 6, 10, 15, 24, 36, 42, 60, 105, 63, 252. What were the five numbers?

(6 points)

This problem is for grade 9 students only.