a, 39*49-39*17
= 39 (49 - 17)
= 39 * 32
= 1248
b,12*53+53*172-53*84
= 53 (12 + 172 -84)
= 53 * 100
= 5300
c,17+18+19+99
= 17 + 17 +1 + 17 +2 + 99
= 3 * 17 + (1+ 99) + 2
= 151 +2
= 153
d, 23+25+49
= 48 + 49
= 97
e,46-45+44-43
= (46 + 44) + (-45 -43)
= 88 + (-88)
= 0