The simplified ratio is 7:6:5.
Ratios represent the proportional relationship between different quantities. In the given ratio 21:18:15, it means that the first quantity is in a relationship of 21 parts, the second quantity is in a relationship of 18 parts, and the third quantity is in a relationship of 15 parts.
To simplify the ratio 21:18:15, you can divide all three numbers by their greatest common factor. In this case, the greatest common factor of 21, 18, and 15 is 3.
So, when you divide each number by 3, you get:
21 ÷ 3 = 7
18 ÷ 3 = 6
15 ÷ 3 = 5
Therefore, the simplified ratio is 7:6:5.