To measure an index card using color tiles,
1. Find the area of one card by finding the length and breadth, which will be equal to Length × Breadth, as cards are in the shape of a rectangle.
2. Find area of any of single color tiles , by measuring the length and breadth if it is in the shape of rectangle, area equal to Length × Breadth otherwise if it is in the shape of square use the formula , area of square = (Side)²
Divide Area of one index card by area of single tile.
If it is an integral value, suppose P
Then, number of color tiles = P
If it is not an integral value, round up to nearest integer
which will be number of color tiles used.