Final answer:
To complete the remaining work in 20 days, working 8 hours per day, we need an additional 75 persons.
Step-by-step explanation:
To find the number of additional persons needed to complete the remaining work in 20 days, working 8 hours per day, we first need to calculate the amount of work done in 10 days by 480 persons working 10 hours per day. Since they completed one-fourth of the work, the total work done by them is 480 * 10 * 10 / 4 = 6,000 units.
Now, let's find the total work remaining. Since 6,000 units have been completed, the remaining work is 1 - 1/4 = 3/4 of the total work.
We can calculate the number of units completed in one day by 480 persons as 6,000 / 10 = 600 units. So, the total work remaining is 600 * 20 = 12,000 units. Since we want to complete this work in 20 days with 8 hours of work per day, we need to find the number of persons required.
Let's solve for the number of additional persons needed: 12,000 / (8 * 20) = 75 persons. Therefore, we need an additional 75 persons to complete the remaining work in 20 days.