Home Back to the Challenge Try These Think About This... Did You Know? Resources Try Another Challenge
Answer
Figure This!
 

Quick Answer:

Since Helix was exposed to the sun for 5 minutes without protection, he had only 3 minutes left before he would burn. A sunscreen with an SPF of 10 would extend the time left to 30 minutes.

 

Complete Solution:

An SPF 10 product used before going in the sun, and when the user normally burns in 8 minutes, provides about 8x10, or 80 minutes of protection.

Putting the lotion on 5 minutes after being in the sun uses 5/8 of the time before being burned. Thus, 3/8 of the normal protection time before burning is left.

Because (3/8)(80) is 30, a person has 30 minutes before burning.

Note: The limits of safe exposure to sunlight vary by individual, season, and geographic location.

  
   
Home · Back to the Challenge · Try These · Think About This  ·  Did You Know? · Resources
Try Another Challenge · Challenge Index · Math Index · Printing the Challenges · En Español
Family Corner · Teacher Corner · About Figure This! · Purchase the CD
©2004 National Council of Teachers of Mathematics
Web site and CD-ROM design/production
© 1999-2004 KnowNet Construction, Inc.