probability
Probability
Level
4
If any four whole numbers are taken at random and multiplied together. The chance that the last digit in the product is 1,3,7 or 9 is a/b. Find b-a ?
The answer is 609.
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1 solution
For the last digit of product, we are only concerned about last digits of the 4 whole numbers..which can vary from 0-9 (10 options)
It is very easy to note that product of numbers can end with 1,3,7,9 only when the numbers itself end in 1,3,7,9.
Any other end digit(0,2,4,5,6,8) will spoil the result.
So for all 4 places we have 4 options out of 10.
Required pprobability = (4/10)⁴
=16/625
So b-a=609