In order to do this, we need to find the area that he needs to cover and the area of each tile.
First, let's find the area he needs to cover. We do this by finding the area of one square, and multiplying that by 5.
20*20*5=2,000
Now, we find the area of one tile. We do this by multiplying the length times the width, or 5*5 = 25. Finally, we divide 2,000/25 to find the number of tiles that we need.
2,000/25 = 80, so Raj will need 80 tiles.