Friday

September 19, 2014

September 19, 2014

Posted by **Jim** on Saturday, May 7, 2011 at 3:05pm.

The books says 127. Could someone please explain this? Thanks

- Math -
**Reiny**, Saturday, May 7, 2011 at 3:29pmSince repetition is allowed, and the 2 must be included, it is easy to forget that the 2 can show up once, twice or even three times

case 1: only one 2

number of ways = 3(6)(6) = 108

(2XX, X2X, XX2, where X is one of the other 6 digits)

case 2: two 2's

number of ways = 3(6) = 18

(22X, 2X2, X22, where X is one of the other 6 digits)

case 3: three 2's , namely 222

number of ways = 1

total = 108+18+1 = 127

- Math -
**Mgraph**, Saturday, May 7, 2011 at 3:32pm127=7^3-6^3

7^3 all 3-digit numbers, formed using

1,2,3,4,5,6,7

6^3 ... using 1,3,4,5,6,7

- Math -
**Reiny**, Saturday, May 7, 2011 at 3:38pmMgraph

Very nice, good logic.

**Answer this Question**

**Related Questions**

Math for Elementary Teachers II - How many 4-digit license plates can be made by...

algebra - Consider making a four-digit I.D. number using the digits 3,5,8, and ...

MATH157 - How many 4-digit license plates can be made by using the digits 0, 2, ...

Math - How many 4-character license plates are possible with 2 letters from the ...

math,correction, bobpursly - Since when is 5^7 =8125? if a number is a multple ...

Math - How many 2-digit numbers can be formed using only the digits 2, 3, 5, and...

math - How many 4-digit numbers can be formed using the digits 1, 2, 3, 4, 5, 6...

Math - Mr. Digit wanted to assign a number to each student in his class. He ...

math,correction - can someone correct this for me parts A-E and if i am wrong ...

holy heart - Using digits 2, 3, 5, 6, 7 and 9, how many 3-digit numbers can be ...