Question
The average number of wafers in Box X, Box Y and Box Z is 31. Box X has 30 wafers. The number of wafers in Box Y is twice the number of wafers in Box Z. What is the number of wafers in Box Z?
2 m

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The average number of wafers in Box X, Box Y and Box Z is 31. Box X has 30 wafers. The number of wafers in Box Y is twice the number of wafers in Box Z. What is the number of wafers in Box Z?