2016 · Q17
A can do 50% more work than B in the same time. B alone can do a piece of work in 30 hours. B starts working and had already worked for 12 hours when A joins him. How many hours should B and A work together to complete the remaining work ?
Elementary MathematicsTime and Work
- A6 hours
- B12 hours
- C4.8 hours
- D7.2 hours
Explanation
A's rate is 1.5 times B's rate of 1/30 per hour, i.e. 1/20 per hour. B's 12 hours complete 12/30 = 2/5 of the work, leaving 3/5. Together they work at 1/30+1/20 = 1/12 per hour, so the remaining work takes (3/5)/(1/12) = 36/5 = 7.2 hours (option D).