ISRO Scientist Time and Work — practice questions — page 2

1. If B does one unit a day, A does two units a day. 2. Together they do 3 units a day. 3. In 8 days they finish the job, so the whole job is 3 x 8 = 24 units. 4. A alone does 2 units a day, so A needs 24 / 2 = 12 days. 5. As a check, B alone would need 24 days, which is twice A's time, exactly as stated. _Source: syllabus Maths, Ch 11 'Direct and Inverse Proportions', S11.3 Inverse Proportion_

1. The inlet fills one sixth of the tank each hour. 2. The outlet removes one eighth of the tank each hour. 3. The net filling rate is 1/6 - 1/8. 4. Over a common denominator of 24 that is 4/24 - 3/24 = 1/24 per hour. 5. So the tank fills in 24 hours. Adding the rates instead of subtracting would give about 3.4 hours, ignoring that one pipe works against the other. _Source: syllabus Maths, Ch 11 'Direct and Inverse Proportions', S11.3 Inverse Proportion_

1. A completes one twentieth of the job each day. 2. In 5 days he completes 5 x 1/20 = 5/20. 3. That simplifies to one fourth of the job done. 4. The work remaining is 1 - 1/4. 5. So three fourths of the job is still left. Answering one fourth reports the part finished, not the part left. _Source: syllabus Maths, Ch 11 'Direct and Inverse Proportions', S11.3 Inverse Proportion_