Question

Number of 4 different digits is formed by using 1, 2, 3, 4, 5, 6, 7. Find the probability that it is divisible by 5.

Answer 1

You can repeat digits, I assume?

Answer 2

yup

Answer 3

Well, then, this is just like drawing from a pool containing all these digits, only everytime you draw, you put it back, right?

Answer 4

?

Answer 5

It's like there's an urn, with 7 chips, one marked 1, one marked 2, etc.
And you pick a chip from that urn, four times, but every time you pick a chip, you put it back.

Answer 6

So actually, it doesn't matter what the first three digits are, just that the last (fourth) digit must be 5, right?

Answer 7

is the solution should be liek this:
total four digit numbers that can be formed by 1 2 3 4 5 6 7 are 7*6*5*4=840
total four digit numbers that can be formed by 1 2 3 4 5 6 7 where last number is 5 are7*6*5=210
probablity is 210/840=1/4

Answer 8

Question... how did you get that the probability of a four digit number with 5 as a last digit is 5?

Answer 9

plse tell me how to solve

Answer 10

First of all, how many possible four digit numbers can you form?
8 x 8 x 8 x 8, right, since digits can be repeated?

Answer 11

k

Answer 12

Nope, I was wrong :D
It's just
7 x 7 x 7 x 7

My bad :D

Answer 13

k

Answer 14

Now, how many of these end with 5?
They're
7 x 7 x 7 x 1, right, since you can only have 5 for your last digit.

Answer 15

k

Answer 16

well, divide
\[\large \frac{7\cdot7\cdot7\cdot1}{7\cdot7\cdot7\cdot7}\]
What do you get?

Answer 17

correct