a, (2015 + 49) - 15
= 2015 - 15 + 49
= 2000 + 49
= 2049
b, (2150 + 1969) - ( 150 + 969)
= 2150 - 150 + 1969 - 969
= 2000 + 1000
= 3000
c, 1568 - (100 + 68)
= 1568 - 68 - 100
= 1500 - 100
= 1400
d, (1586 + 2005) - 1586
= 1586 - 1586 + 2005
= 0 +2005
= 2005