How many three-digit odd integers less than 500 are there so that all the digits are not distinct?
A. 56
B. 88
C. 144
D. 200
E. 250
Number of odd integers
This topic has expert replies
GMAT/MBA Expert
- Anju@Gurome
- GMAT Instructor
- Posts: 511
- Joined: Wed Aug 11, 2010 9:47 am
- Location: Delhi, India
- Thanked: 344 times
- Followed by:86 members
While attacking counting problem always satisfy the restrictions first, so that you can freely select the rest. Here the restrictions are,psm12se wrote:How many three-digit odd integers less than 500 are there so that all the digits are not distinct?
- 1. Integers must be less than 500 ---> First digit can be either 1, 2, 3, or 4.
2. Integers must be odd ---> Last digit can be either 1, 3, 5, 7, or 9.
If we can calculate the number of three-digit odd integers less than 500 with all the digits different and subtract that from 200, we will have our answer.
Number of three-digit odd integers less than 500 with all the digits different...
- Numbers starting with 1 ---> (4 choice for last digit)*(8 choice for middle digit) --> 32
Numbers starting with 2 ---> (5 choice for last digit)*(8 choice for middle digit) = 40
Numbers starting with 3 ---> Same as numbers starting with 1 --> 32
Numbers starting with 4 ---> Same as numbers starting with 2 --> 40
The correct answer is A.
Anju Agarwal
Quant Expert, Gurome
Backup Methods : General guide on plugging, estimation etc.
Wavy Curve Method : Solving complex inequalities in a matter of seconds.
§ GMAT with Gurome § Admissions with Gurome § Career Advising with Gurome §
Quant Expert, Gurome
Backup Methods : General guide on plugging, estimation etc.
Wavy Curve Method : Solving complex inequalities in a matter of seconds.
§ GMAT with Gurome § Admissions with Gurome § Career Advising with Gurome §
- GMATGuruNY
- GMAT Instructor
- Posts: 15539
- Joined: Tue May 25, 2010 12:04 pm
- Location: New York, NY
- Thanked: 13060 times
- Followed by:1906 members
- GMAT Score:790
Integers with all 3 digits NOT distinct = total number of integers - integers with all 3 digits distinct.psm12se wrote:How many three-digit odd integers less than 500 are there so that all the digits are not distinct?
A. 56
B. 88
C. 144
D. 200
E. 250
Total number of integers:
To count consecutive integers:
Number of integers = biggest - smallest + 1.
Thus, from 100 to 499, inclusive:
Number of integers = 499 - 100 + 1 = 400.
Integers with all 3 digits distinct:
Number of options for the hundreds digit = 4. (1, 2, 3 or 4).
Number of options for the tens digit = 9. (Any digit 0-9 but the digit already used.)
Number of options for the units digit = 8. (Any digit 0-9 but the 2 digits already used.)
To combine these options, we multiply:
4*9*8 = 288.
Thus, from 100 to 499, inclusive:
Number of integers with all 3 digits NOT distinct = 400-288 = 112.
Of these 112 integers, exactly HALF will be odd:
112/2 = 56.
The correct answer is A.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3