Minus' Solution to

Kewl CDs
Posted June 17 - 23, 1996

Kevin has 25 kewl CDs, including some from up-and-coming garage bands. Nine of the CDs play for less than 20 minutes. Twelve play for more than 30 minutes. Four play for more than 40 minutes. What is the total number Kevin's CDs that play between 30 and 40 minutes?

Since 9 play for less than 20 minutes, and 12 play for more than 30 minutes, there are 4 that play between 20 and 30 minutes.

Since 12 play for more than 30 minutes, and 4 play for more than 40 minutes, 8 play between 30 and 40 minutes.
Your Solutions

Norma Komplin of Houston, TX [komplin@ruf.rice.edu] impressed Minus with this perfect solution:

8 of Kevin's CDs play between 30 and 40 minutes.

Since 9 of the CD's play for less than 20 min and 4 play for more than 40 min., this narrows the CD's which play for 30-40 min to a maximum of 12 (25-(9+4)). Of the 12 CD's which play for more than 30 min 4 play for more than 40 min leaving 8 CD's between 30-40 min.

Minus received answers ranging from 0 CDs to 16 CDs.
These were incorrect, but he loved chewing on them anyways.

Thanks to everyone who submitted solutions.
Keep up the great work!