3.
a)
[tex]357 + 98 = 457 - 2 = 455\ \ \rightarrow \ \ 357+98 = 357 + 100 + (100-98) = 457-2 = 455[/tex]
[tex]327 + 96 = 427 -4 = 423\\\\1278+94 = 1378-6 = 1372[/tex]
b)
[tex]548 + 297 = 848-3 = 845\\\\536+497 = 1036 -3 = 1033\\\\1385+395 = 1785-5 = 1780[/tex]
4.
a)
[tex]23\cdot 4 = 46\cdot2 = 92\\\\92\cdot4 = 184\cdot2 = 368\\\\235\cdot4 = 470\cdot 2 = 940[/tex]
b)
[tex]17\cdot6 = 34\cdot3 = 102\\\\29\cdot6 = 58\cdot3 = 174\\\\56\cdot6 = 112\cdot3 = 336[/tex]
