=-9+20-2 1
=- 10
2.(-42 points 1)÷(6 points 1- 14 points 3+3 points 2-7 points)
=(- 1/42×42)÷42*( 1/6-3/ 14+2/3-2/7)
=- 1÷(7-9+28- 12)
=- 1÷ 14
=- 1/ 14
3.999 and 8/9 (-2+8/9)
=( 1000- 1/9)÷(- 18/9+8/9)
=( 1000- 1/9)×(-9/ 10)
=-900+ 1/ 10
=-899 and 65438+9/00
4.(-49)÷(2 1/3) * 3/7 * (-3 1)
=(-49)÷(7/3)×(3/7)×(- 1/3)
=(-49)×(3/7)×(3/7)×(- 1/3)
=3