What is the probability of correctly guessing a 7 number random code out of 20 numbers (i.e. 1-20)? The probability needs to be expressed as in 1:1000. Thanks
The probabillity of guessing correctly should be:
1/20 x 1/19 x 1/18 x 1/17 x 1/16 x 1/15 x 1/14 =1: 390,700,800
+37191 Guest 1 shows the answer if you cannot use the numbers 1-20 more than once
If you CAN use the numbers more than once, it is MUCH larger
20 x 20 x 20 x 20 x 20 x 20 x 20 = 20^7 =20^7 = 1280000000 or 1: 1,280,000,000
+118725 What is the probability of correctly guessing a 7 number random code out of 20 numbers (i.e. 1-20)? The probability needs to be expressed as in 1:1000. Thanks
This question is worded badly because the title asks for a 7 digit code but some of the numbers in the code are 2 digits - this does not make sense.
Anyway....
If the numbers have to be in the right order and there is repeat allowed then it will be
1/20^7 = 0.00000000078125
0.00000000078125*1000 = 0.00000078125
so that is a chance of 0.00000078125 in 1000
I do not like your chances of guessing correctly 
Brilliant responses, many thanks everybody.
The numbers wouldn't be allowed to be used more than once in the code to clarify, so the code would be something like 8-5-3-4-11-18-19 out of a list of 20 numbers from 1-20.
So, from that it sounds as though the correct answer would be 1: 390,700,800?
So, pretty improbably then I would guess!
