a. 84 : 4 + 39 : 37 + 50
= 21 + 32 + 1
= 21 + 9 + 1
= 21 + 10 = 31
b. 2010 - 2000 : [ 486 - 2.(72 - 6) ]
= 2010 - 2000 : [ 486 - 2.(49 - 6) ]
= 2010 - 2000 : ( 486 - 2.43 )
= 2010 - 2000 : ( 486 - 86 )
= 2010 - 2000 : 400
= 2010 - 5
= 2005
c. 62 - 120 + (-5) - |-5|
= 36 - 120 - 5 - 5
= 36 -