T can complete a work in 20 days and U can complete the same work in 10 days. If both of them work together, then in 4 days what percent work of the total work will be completed?

Let the total work be represented by $$1$$ unit.

Work rate of T = $$\frac{1}{20}$$ unit/day (because T finishes the whole work in 20 days).

Work rate of U = $$\frac{1}{10}$$ unit/day (because U finishes the whole work in 10 days).

When they work together, their combined rate is the sum of individual rates:
$$\frac{1}{20} + \frac{1}{10} = \frac{1}{20} + \frac{2}{20} = \frac{3}{20}$$ unit/day.

Work completed in 4 days = rate × time
$$\frac{3}{20} \times 4 = \frac{12}{20} = \frac{3}{5}$$ of the total work.

Fraction $$\frac{3}{5}$$ equals $$\frac{3}{5} \times 100 = 60\%$$.

Therefore, 60 percent of the work will be completed in 4 days.

Option D which is: 60 percent