GMAT question of the day

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Type: Problem Solving

Difficulty: 2 star rating

Karen, Leonard, Mary and Nicholas each working alone can sew 100 buttons onto shirts in 2, 3, 4 and 6 hours respectively. How long would it take for Karen, Leonard, Mary and Nicholas to sew 100 buttons onto shirts all working together?

15 minutes
42 minutes
48 minutes
50 minutes
1 hour