The ratio of the ages of father and son is 9:2 if the father is 45 year old, find the son

If the ratio is 9:2 that means that 45 would by ñ times 9. At the same time, ñ must also fit the ratio. Using this knowledge, you can divide 45 by 9, giving you 5, then multiply it by 2. This means that the child is 10 years old.