Problem 47. Area

On an infinite grid, draw a square whose area is 5 times that of a square on the grid. Use a straight-edge but not a compass.

Problem 46. Ostriches and giraffes

A zoo has several ostriches and several giraffes. They have 30 eyes and 44 legs. How many ostriches and how many giraffes are in the zoo?

Problem 45. Cub with a hole

Is it possible to build a cube 3x3x3 with a hole 1x1x1 in the center using 13 bricks 1x1x2 ?

Hint. Paint bricks and cube in two colors, count number of small cubes 1x1x1 of each color.