A system goes from P to Q by two different paths in the P-V diagram as shown in the figure. Heat given to the system in path 1 is 1000 J. The work done by the system along path 1 is more than path 2 by 100 J. What is the heat exchanged by the system in path 2?

Hint: Use the first law of thermodynamics.
Step 1: Write down the given data.
For path 1, Heat given, Q1 = + 1000J
                 Work done, = W1(let)
For path 2,
                Work done (W2)=(W1-100)J
                Heat given, Q2=?
Step 2: Use the first law of thermodynamics.
As the change in internal energy between two states for different path is the same,
                         U=Q1-W1=Q2-W2
                         100-W1=Q2-(W1-100)
                           Q2=1000-100=900J