An improper fraction has a numerator larger than its denominator (e.g. $\frac{7}{3}$). A mixed number combines a whole number and a proper fraction (e.g. $2\frac{1}{3}$). You need to convert fluently between the two forms.
Improper fraction → mixed number: divide the numerator by the denominator. The quotient is the whole number part; the remainder is the new numerator.
$$\frac{7}{3} = 2\text{ remainder }1 = 2\tfrac{1}{3}$$
Mixed number → improper fraction: multiply the whole number by the denominator, then add the numerator. Keep the same denominator.
$$2\tfrac{1}{3} = \frac{(2 \times 3) + 1}{3} = \frac{7}{3}$$
Always convert mixed numbers to improper fractions before multiplying or dividing — arithmetic with mixed numbers in their original form is error-prone.
Common error: adding the whole number to the numerator rather than multiplying when converting — always multiply first.