20.1 problem 546
 20.2 problem 547
 20.3 problem 548
 20.4 problem 549
 20.5 problem 550
 20.6 problem 551
 20.7 problem 552
 20.8 problem 553
 20.9 problem 554
 20.10 problem 555
 20.11 problem 556
 20.12 problem 557
 20.13 problem 558
 20.14 problem 559
 20.15 problem 560
 20.16 problem 561
 20.17 problem 564
 20.18 problem 565
 20.19 problem 566
 20.20 problem 567
 20.21 problem 568
 20.22 problem 569
 20.23 problem 570
 20.24 problem 571
 20.25 problem 572
 20.26 problem 573
 20.27 problem 574
 20.28 problem 575
 20.29 problem 576