A Class 6 section collected ₹450 for a plantation drive and spent $\frac{2}{9}$ of it on saplings. How much was spent on saplings?

A fraction a/b says: the whole is split into b equal parts, and we are talking about a of them. So 3/8 means: divide the whole into 8 equal parts, take 3 of them. The two equal parts is what makes it a fraction — three slices of an unevenly cut cake do not give you 3/8. The denominator must always be a positive whole number. The numerator can be 0, equal to the denominator (giving 1), greater than the denominator, or less than it.