Home › NDA › Quantitative Aptitude › Time and Work › A and B together finish a job in 12 days. A alon…
A and B together finish a job in 12 days. A alone takes 20 days. B alone would take:
A24 days
B28 days
C30 days
D32 days
Answer & Solution
Correct answer: C. 30 days
1. Together they complete one twelfth of the work each day.
2. A alone completes one twentieth each day.
3. So B's daily share is 1/12 - 1/20.
4. Taking 60 as the common denominator, that is 5/60 - 3/60 = 2/60, which is one thirtieth.
5. B alone therefore needs 30 days, which is sensibly slower than A.
_Source: NCERT Class 8 Maths, Ch 11 'Direct and Inverse Proportions', S11.3 Inverse Proportion_
Related questions
Those two workers, at that combined rate, finish the whole job in:A worker finishing in 5 hours and another in 20 hours together do what share of the job eaConverting two fifths of an hour into minutes gives:In work problems, the parts of the job done by each worker in one hour add up to:Flying into that same 30 mph wind, the same plane's ground speed would be:A plane's ground speed with a tailwind of 30 mph, if the plane itself flies at 150 mph, isOn that drive, Tony's interstate speed was:Tony drives 4 hours in all, 208 miles on the interstate and 40 on country roads, going 15