Chapter     Some suggested problems...
     15        5,7,9,10,14,27,33,40,44,50,53,55,57,61                              
     16        4,8,10,11,17,19,21,31,37,40,46,58,60,64                             
     17        9,11,13,16,22,32,34,36,39,40,47,55,59,60                            
     18        8,10,11,15,23,29,34,36,41,42,43,46,55,61                            
     19        4,6,7,22,24,26,28,32,42,46,58,63,78                                 
     20        4,6,11,20,23ab,27,33,46a,52,58,62,73
     21        4,5,11,29,31,33a,34c,40a,42,49,52,53,62,63
     22        2a,3cd,10,18,19a,35,38 ( extras 43,53ab) 
     23        20,29,31ab,37,44,51
     24        4,10abc,12,22,28a,29a
     25        4ab,5abc,13ab,18ab,22
     26        5,15,22,24,25,29,30,32,35,42,44,45