Question

Number of 3digit number with exactly two 6's

Answer 1

Answer:

I assume that this requires a combinatorial, so I think that what I need to do (26) since if we pick the first few the first two digits to be 1's and the second two digits to be 2 we only need to account for the last set of two. In this case the answer would be 15

The book I'm using says the answer is 90. I don't understand this.

In the following example provided in the book

Step-by-step explanation:

i hope you understand

Answer 2

Heya,

Number of 3 digit number with exactly two 6's is 26

Case 1 :- The hundreds and tens are 6.

The ones can be changed in 9 ways.(0,1,2,3,4,5,7,8,9)

Case 2 :- The hundredts and ones are 6.

The tens can be written in 9 ways .

Case 3:- Ones and tens are 6.

The hundreds can be written in 8 ways (1,2,3,4,5,7,8,9)

Hence, the total number is 26.

Regards

Kshitij