[Q.1] How many 4-digit numbers can be formed by using the digits 0-9, so that no two digits are repeated?
(A) 4536 (B) 4546 (C) 4556 (D) 9436 (E) 9556
[Q.2] How many even 4-digit numbers can be formed by using the digits 0-9, so that no two digits are repeated?
(A) 2296 (B) 2396 (C) 2444 (D) 2456 (E) 2486
[Q.3] How many even 4-digit numbers divisible by 4 can be formed by using the digits 0-9, so that no two digits are repeated?
(A) 336 (B) 784 (C) 1120 (D) 1804 (E) 1936
[Q.4] How many 4-digit numbers can be formed by using the digits 0-9, so that the numbers contains exactly 3 distinct digits?
(A) 1944 (B) 3240 (C) 3850 (D) 3888 (E) 4216
For Q.1, I am getting [spoiler](A) 4536[/spoiler] as the answer.
Counting: 4 problems on 4-digit numbers
This topic has expert replies
- neerajkumar1_1
- Master | Next Rank: 500 Posts
- Posts: 270
- Joined: Wed Apr 07, 2010 9:00 am
- Thanked: 24 times
- Followed by:2 members
A1) 9 * 9 * 8 * 7 = 4536
IMO: A
starting from left to right
the first digit has 9 choices i.e from 1 to 9 since the number is a 4 digit number
the rest have a option of 10 choices i.e from 0 to 9 minus the number of digits previously chosen..
IMO: A
starting from left to right
the first digit has 9 choices i.e from 1 to 9 since the number is a 4 digit number
the rest have a option of 10 choices i.e from 0 to 9 minus the number of digits previously chosen..