The subsets of the set {w, x, y} are {w}, {x}, {y}, {w, x}, {w, y}, {x, y}, {w, x, y}, and { } (the empty subset). How many subsets of the set {w, x, y, z} contain w ?
four
five
seven
Eight
sixteen
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除了W外的元素，从剩下三个元素里选。c(3,0)+c(3,1)+c(3,2)+c(3,3)=8
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除了W外的元素，从剩下三个元素里选。c(3,0)+c(3,1)+c(3,2)+c(3,3)=8
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