A can finish a job in 20 days. After working 5 days he leaves. The fraction of work left is:

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: NCERT Class 8 Maths, Ch 11 'Direct and Inverse Proportions', S11.3 Inverse Proportion_