5x + 1 + 2 + 3 + 4 + 5 = 115
5x + 15 = 115
x = 115 : 15
x = bạn tư tính
( x + 1 ) + ( x + 2 ) + ( x + 3 ) + ( x + 4 ) + ( x + 5 ) = 115
X x 5 + ( 1 + 2 + 3 + 4 + 5 ) = 115
X x 5 + 15 = 115
X x 5 = 115 - 15
X x 5 = 100
X = 100 : 5
X = 20
( X + 1 ) + ( X + 2 ) + ( X + 3 ) + ( X x 4 ) + ( X + 5 ) = 115
X x 5 = 115 - 5 - 4 - 3 - 2 - 1
X x 5 = 100
X = 100 : 5
X = \(15\)
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