Anurag@Gurome wrote:harrybm wrote:Can Anyone help me with this Problem:
How many Positive integers less than 10000 are there, in which the sum of the digit equal to 5?
a) 31
b) 51
c) 56
d) 62
e) 93
Can anyone help pleasee??
We need to find integers between 0 to 9999, in which the sum of digits adds up to 5.
(1) One digit is 5 and all other are 0: 0005, 0050, 0500, 5000 or we can say that no. of ways we can arrange the digits = 4!/3! = 4 ways
(2)Three 1's and one 2: 1112, this can be done in 4!/3! = 4 ways
(3) One 4 and one 1: 4100, this can be done in 4!/2! = 12 ways
(4) One 3 and one 2: 3200, this can be done in 4!/2! = 12 ways
(5) One 3 and two 1's: 3110, this can be done in 4!/2! = 12 ways
(6) Two 2's and One 1: 2210, this can be done in 4!/2! = 12 ways
Therefore, required number of positive integers = (12 * 4) + (4 * 2) = 48 + 8 = 56
The correct answer is
C.
Thank you Anurag, GMATGuruNY and AnurangSahu for the comprehensive explanation. However I'm always confused every time I see tough counting problems, especially to figuring out the approach in the beginning? Do you have any tips on this? (maybe any method to cluster problems on specific type, etc?)
Moreover I have further question in related topic:
There are 6 people sitting together, A, B, C, D, E, F. and A doesn't want to sit with B. How many arrangement can be made?
1) I understand I can solve like this:
Total Outcome - total outcome of 5 arrangement x 2 (since A & B interchangeable)
6! - (5! x 2) = 480 arrangement
But why cant I solve it like this:
6! - 6!/2! ?
6! is the total outcome
6!/2! is the total outcome considering 2 of them are interchangeable like word: PIZZA, since Z is interchangeable there are 5!/2! = 60 outcomes.
Please advice where do I go wrong here? and is there any alternative approach beside the first method? Thank you before
