An electronic store receives a shipment of 20 graphing calculators including 6 that are defective. Four of the calculators are selected to be sent to a local high school. How many of these selections will contain no defective calculators

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Selecting 30 out of 4, that means 30C4, or C(30,4) or combination (30, 4).

30! / (4! (30-4)!)
= 30x29x28x27 / (4x3x2x1) 

Select all 4 from the set of 27 good calculators to get no defective calculators. Thank you for posting your question. I hope that this answer helped you. Let me know if you need more help.