257×A+142×A+A-A×100=4500

=> A × ( 257 + 142 + 1 - 100 ) = 4500

=> A × 300 = 4500

=> A = 4500 : 300

=> A = 15

a) (−1)[52−(43)]=(−1)(25−64)=(−1)(−39)=39(−1)[52−(43)]=(−1)(25−64)=(−1)(−39)=39

b) 71.64−32.(−7)+32.11=142.32+32.7+32.1171.64−32.(−7)+32.11=142.32+32.7+32.11

=32.(142+7+11)=32.(142+18)=32.160=5120=32.(142+7+11)=32.(142+18)=32.160=5120

c) 666−(−422)−100−88=666+422−100−88666−(−422)−100−88=666+422−100−88

=(666+422)−(100+88)=1088−188=900=(666+422)−(100+88)=1088−188=900

d) 23−501−343+61−257+16−49923−501−343+61−257+16−499

=(23+61+16)−(501+499)−(343+257)=(23+61+16)−(501+499)−(343+257)

=100−1000−600=100−(1000+600)=100−1600=−1500