document.write( "Question 346191: A student needs eight chips of a certain type to build a circuit. It is known that 5% of these chips are defective. How many chips should he buy for there to be a greater than 90% probability of having enough chips for the circuit? \n" ); document.write( "
Algebra.Com's Answer #247675 by nyc_function(2741)\"\" \"About 
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Clearly he must buy at least 8. The probability that all 8 will be nondefective is\r
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\n" ); document.write( "\n" ); document.write( "(8 choose 8) (0.95)^8 (0.05)^0 ≈ 0.66342\r
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\n" ); document.write( "\n" ); document.write( "So, 8 is not enough.\r
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\n" ); document.write( "\n" ); document.write( "The probability that 8 of 9 will be nondefective is\r
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\n" ); document.write( "\n" ); document.write( "(9 choose 8) (0.95)^8 (0.05)^1 ≈ 0.29854\r
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\n" ); document.write( "\n" ); document.write( "The probability that 9 of 9 will be nondefective is\r
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\n" ); document.write( "\n" ); document.write( "(9 choose 9) (0.95)^9 (0.05)^0 ≈ 0.63025\r
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\n" ); document.write( "\n" ); document.write( "The probability that either 8 or 9 will be nondefective is \r
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\n" ); document.write( "\n" ); document.write( "0.29854 + 0.63025 = 0.92879 > .90\r
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\n" ); document.write( "\n" ); document.write( "So, 9 chips should be enough.
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