(1)20.01X20.02-20.00X20.03
=20.01X20.02-20.00X20.02-20.00X0.01
=20.02X(20.01-20.00)-20.00X0.01
=20.02X0.01-20.00X0.01
=0.01X(20.02-20.00)
=0.01X0.02
=0.0002
(2)100X7.9+184X2.1+84X7.9
=7.9X(100+84)+184X2.1
=7.9X184+184X2.1
=184X(7.9+2.1)
=184X10
=1840