24is ther any other method than direct counting??
A number is seelceted randomly from 3 digit nos. 100,101...........999 .The prob that in the selected no. at least one of the digits is 9 is??
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UP 0 DOWN 0 0 12
12 Answers
621- p that none is 9
prob 1st digit is not 9 =8/9
prob 2nd digit is not 9 is 9/10
prob 3rd digit is not 9 is 9/10
total prob = 1-8/9 x 9/10 x 9/10 =1-72/100 = 28/100!
11[ (1/9)*(9/10)*(9/10) + (8/9)*(1/10)*(9/10) + (8/9)*(9/10)*(1/10) + (1/9)*(1/10)*(9/10) + (8/9)*(1/10)*(1/10) + (1/9)*(9/10)*(1/10) + (1/9)*(1/10)*(1/10) ] = (9(9+8+8+1+1) + 8+1)/900 = 252/900 = 28/100 = 7/25 (same ans. as above!!)
7/25 < 6/15
7/25 < 1/3
7/25 < 1/3
7/25 < 3/4