Why the answer of the ratio of 25 cm to 9 dm is 518?

The ratio of 25 cm to 9 dm is not 518. To find the ratio, first convert both measurements to the same unit. Since 9 dm is equal to 90 cm, the ratio becomes 25 cm to 90 cm. Simplifying this gives a ratio of 25:90, which can be reduced to 5:18, not 518.