19.
a) (243 + 597) + (1996 - 243 - 597)
= 243 + 597 + 1996 - 243 - 597
=(243 - 243) + (597 - 597) + 1996
= 0 + 0 + 1996
= 1996
b) (178 - 1936) - [(-1936) - (-178)]
= 178 - 1936 + 1936 - 178
= (178 - 178) + ( -1936 + 1936)
= 0 + 0
= 0
c) (1567 + 894) + (2004 - 894 - 1567)
= 1567 + 894 + 2004 - 894 - 1567
= (1567 - 1567) + (894 - 894) + 2004
= 0 + 0 + 2004
= 200
d) (1932 - 2476) - (932 - 476)
= 1932 - 2476 - 932 + 476
= (1932 - 932) + (-2476 + 476)
= 1000 + -2000
= -1000
