A student incorrectly calculated $5\frac{1}{3} \div 2\frac{1}{2}$ by computing the whole numbers and fractions separately. What is the main error in this approach?

The reciprocal of the dividend was used instead of the divisor.

The mixed numbers were not converted to improper fractions before dividing.

The whole numbers were multiplied instead of divided.

The final answer was not simplified correctly.

Which expression shows the correct step after converting the mixed numbers to improper fractions for $4\frac{1}{5} \div 2\frac{1}{3}$?

$\frac{21}{5} \times \frac{7}{3}$

$\frac{5}{21} \times \frac{3}{7}$

$\frac{21}{5} \times \frac{3}{7}$

$\frac{5}{21} \times \frac{7}{3}$

They added the whole number to the numerator.

They multiplied the numerator by the denominator.

They forgot to include the whole number.

They inverted the fraction after converting.