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

• abcd = 1, 3, 7, 9 (10)
  or a, b, c, d 5 (10)
  
  Answer = 4^4/10^4 = 16/625
  option c
• 10 years agoHelpfull: Yes(0) No(0)
• 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
• 10 years agoHelpfull: Yes(0) No(0)
• 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
  
• 9 years agoHelpfull: Yes(0) No(1)