2022 · Q14
480 persons working 10 hours per day complete one-fourth of a work in 10 days. How many additional persons are to be employed in order to complete the remaining work in 20 days, working 8 hours per day?
Elementary MathematicsTime and Work
- A400
- B420
- C480
- D500
Explanation
480×10×10 = 48000 man-hours complete one-fourth of the work, so the whole work is 192000 man-hours and 144000 remain. At 8 hours/day for 20 days each worker contributes 160 hours, so 144000/160 = 900 workers are needed; 900 − 480 = 420 additional workers. The keyed option is B.