a, 5x4y chia hết cho 9 và chữ số hàng trăm gấp 2 lần chữ số hàng đơn vị
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b, 42x5xy vừa chia hết cho 5 ,vừa chia hết cho 9
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a: y=3; x=6
b; Sửa đề: 42x5y
y=0 =>x=7
y=5 =>x=2
