Bài 1:
a, (x+19).20=200
x + 19 = 200 : 20
x + 19 = 10
x = -9
b, x+1+x+2+x+3+...+x+100=5050
X x 100 + 5050 = 5050 { X x 100 + ( 1 + 2 + 3 +... + 100)}
X x 100 = 0
X = 0 : 100 = 0
2. a)13*27+27*19+27*73
= ( 13 + 19 + 73 ) * 27
= 105 * 27
= 2835
b, 20*10+40*40
= 200 + 1600
= 1800