maths
posted by sahar .
Hexagonal tiles of sides20cm are used to tile a room which measures 6.25m. Assuming we complete the edges by cutting up tiles, how many tiles are needed?

You need to provide more than one linear dimension for the room. Is the room square or rectangular? Is the 6.25 m number supposed to be SQUARE meters? If so, you should so designate.

Its rectangular room of 6.25m by 4.85m

The distance between opposite sides of the hexagons will be 20sqrt3 = 34.64 cm.
If hexagon edges are parallel to the long wall, you need 4.85/0.3464 = 14 tiles along the short wall. Along the long wall, adjacent pairs take up 0.60 m, so you need 6.25/0.60 = 10.42 pairs or 21 staggered rows. Ten of those rows will require halfhexagons at the ends, but you can use both halves of a cut one.
I claim the answer is 21x14 = 294 tiles. See what you get.
If you just divided the area of the room by the area of each tile, you would get 292, but that would assume no pieces wasted. I would order 300 times to be safe.