Probability Ext 1 hard question (1 Viewer)

[mr.habibbi]

Hi Mathematicians,

I need help on question D, i think it's impossible to solve.

Question asks: a 5 digit number is chosen at random. Find the probability:

d) that the digits are distinct and in increasing order.

Good luck!

 

[Ood]

Just choose any 5 digits from 1 to 9 (omit 0 since your number has to have digits in increasing order, and we don't want 0 at the front)
So 9C5, and there's only 1 arrangement of them which is in ascending order. Total number of 5 digit numbers = 9*10^4 (since 0 can't be at the front)
Thus P = 9C5/9*10^4 = 7/5000

 

[tickboom]

Is there a little ambiguity here? Does increasing order mean always increasing by 1? For example, 12345, 23456, 34567, 45678 and 56789. Or could it also include examples like 13456, 14567, 15678, 16789?

 

[CM_Tutor]

Is there a little ambiguity here? Does increasing order mean always increasing by 1? For example, 12345, 23456, 34567, 45678 and 56789. Or could it also include examples like 13456, 14567, 15678, 16789?

Increasing order allows for examples like 13579, etc.