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| Math Central | Quandaries & Queries |
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Question from Spence, a parent: My son has a problem that he has been unable to figure out. I was asked to try, but I am confused on how to get the last two parts. Any help would be great. How many four-digit numbers can be formed under each condition? A) The leading digit cannot be zero: 9(10)(10)(10)=9000 B) The leading digit cannot be zero and no repetition of digits allowed: 9(9)(8)(7)=4536 C) The leading digit cannot be zero and the number must be less than 5000: ?? D) The leading digit cannot be zero and the number must be even: ?? |
Hi Spence,
C) is very much like A) with the one difference that the number must be less than 5000 so the only choices for the first digit are 1, 2, 3 and 4.
D) again is similar to A) but the to be even the last digit must be even. Thus the last digit must be 0, 2, 4, 6 or 8.
I hope this helps,
Penny
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