Bài 8A : Thực hiện phép tính ( tính hợp lí nếu có thể )
a/ 72.121+27.121+121
b/100 + 97 + 94 + ..... + 4 +1
Bài 10A : Tìm x biết
a/ ( x - 29 ) - 11 = 0
b/ ( x + 5 ) : 3 - 11 = 4
c/ 231 + ( 312 - 2x ) = 531
Bài 10B : Tìm x biết 
a/ ( 50 - x ) + 12 = 31
b/ 75 : ( x - 2 ) + 4 = 7
c/ 125 - 3 ( x + 3 ) = 65 
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