Latest Self Aptitude Question SOLUTION: If 4 whole numbers are taken at random, and multiplied together, then the probability that the last digit in the product is 1,3,7 or9 will be (a)13/976 (b)17/529 (c)16/625 (d)13/6

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(#M40037496) SELF Category question Probability Keep an EYE

If 4 whole numbers are taken at random, and multiplied together, then the probability that the last digit in the product is 1,3,7 or9 will be
(a)13/976 (b)17/529 (c)16/625 (d)13/625

Vaibhav (9 years ago)

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Mayank Sharm  (9 years ago)

abcd = 1, 3, 7, 9 (10)
or a, b, c, d 5 (10)

Answer = 4^4/10^4 = 16/625
option c

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vandana  (9 years ago)

3,7,9 are not possible in the unit place wen 4 whole numbers are multiplied togethr,only 1 i s possible,if the number chosen hav 1,3(3*3*3*3=81-1 as unit place),7(7*7*7*7=1 in unit place),9(9*9*9*9=1 in unit place)
so,possibilities of 1,3,7,9 in unit place of 4 number is 4C1*4C1*4C1*4C1=4*4*4*4=256..
thus numbers are=>1,11,21,31,41,51,61,71,81,91 with 1 in unit place.:=10 possibilities.
similarly,3,13,23,33,43,53,63,73,83,93:=10 possibilities
likewise 7,17,27,37,47,57,67,77,87,97:=10 poss.
and 9,19,29,39,49,59,69,79,89,99:=10 poss.
total posibilties:=10*10*10*10=10000
probability is 4^4/10^4=256/10000=16/625

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ARKAJIT NANDY  (8 years ago)

we get 1,7,3,9 in units place by multiplying only these four(1,7,3,9) no

1----> 1X1 or 7X3
7----> 1X7 or 9X3
3----> 1X3
9----> 1X9 or 3X3
its like
(1st no)X(2nd no)X(3rd no)X(4th no)
now choosing of 1st no=choose any one from 1,7,3,9
so probability of choosing 1st no=4/10
similarly
2nd no=4/10
3rd no=4/10
4th no=4/10

so probability=(4/10)X(4/10)X(4/10)X(4/10)
=16/625

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