[tex]1. \: a) \: 40 - (7 \times 4 )- 12 \\ = 40 - 28 - 12 \\ = 12 - 12 \\ = 0[/tex]
[tex]1b. \: \: 21 \times (16 - 8) \div 3 \\ 21 \times 8 \div 3 \\ 168 \div 3 \\ 56[/tex]
[tex]1c. \: \: (78 - 13) \div 5 \times 6 \\ (65 \div 5) \times 6 \\ 13 \times 6\\ 78[/tex]
[tex]1d. \: \: 108 \div (24 + 12) + 7 \\ (108 \div 36) + 7 \\ 3 + 7 \\ 10[/tex]
[tex]2a. \: \: 16 - ( - 7) + 9 \times ( - 4) \\ 16 + 7 + (9 \times ( - 4)) \\ 1 6+ 7 + ( - 36) \\ 16 + 7 - 36 \\ 23 - 36 \\ - 13[/tex]
[tex]2b. \: \: 125 \div (15 - ( - 10)) + 25 \\ 125 \div (15 + 10) + 25 \\ (125 \div 25) + 25 \\ 5 + 25 \\ 30[/tex]
[tex]2c. \: \: 648 \div ( - 18) - ( - 11) \times ( - 8) \\ (648 \div ( - 18)) + 11 \times ( - 8) \\ - 36 + (11 \times ( - 8)) \\ - 36 + ( - 88) \\ - 36 - 88 \\ - 124[/tex]
[tex]2d. \: \: (34 \times 8 )+ 420 \div 7 - 156 \\ 272 + (420 \div 7) - 156 \\ (272 + 60 )- 156 \\ 332 - 156 \\ 176[/tex]
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