In: Statistics and Probability
Randomly select a 7 digit natural number.
a) Find the probability that the number has 4 odd digits, 3 even
numbers, and no number is repeated.
b) Find the probability that the number 2 is present exactly 2
times, the number 3 is present exactly 3 times, the remaining
digits are present no more than 1 time.
a) We have there are 5 even numbers (0,2,4,6,8) and 5 odd numbers (1,3,5,7,9). Note that 0 is even. The number has 4 odd digits, 3 even numbers, and no number is repeated. The number of possible numbers with this feature is
From this number we have to subtract those numbers starting with 0. The number of 7 digit numbers starting with 0 is
The possible number of 7 digit natural numbers are . (Exclude numbers starting with 0).
Thus the required probability is
b) The number 2 is present exactly 2 times, the number 3 is present exactly 3 times, the remaining digits are present no more than 1 time. The number of possible numbers with this feature is
From this number we have to subtract those numbers starting with 0. The number of such 7 digit numbers starting with 0 is
Thus the required probability is