Dividing and Real Life

  I've given several rate, time, and distance problems to the students as part of their warm-up and an interesting topic popped up. Although the answer is in decimal form is it really a reasonable answer for the situation.

For instance, if you travel 1200 miles while going 65 mph, it is going to take you 18.4 hours but are you really going to tell people that.  You are more likely to say it took almost 18 1/2 hours. 

Airlines usually record the theoretical time as 5 hours, 20 min rather than 5 1/3 hours while most people would state the flight was just under 5 1/2 machines.  Another situation is when you are trying to calculate the number of cocoa beans per candy bar.  It might say 140 cocoa beans are used in a pound of chocolate but if you ask how many cocoa beans in a 2 oz bar of chocolate, you'd get 17.5 beans. 

Again this is a situation where we are more likely to say just over 17 beans per bar or averages 17.5 beans because people don't like working with decimals.  What about planning the amount of paint, carpet, ceiling tiles, etc for a house.

We seldom buy 3.2 gallons of paint.  Most people buy 3.5 gallons or 4 gallons of paint so you have plenty to complete the job.  Other times you may only need 2.6 boxes of tile but you buy 3 boxes because they don't sell a portion of a box, they sell the whole box.

So I work on teaching students to do the actual math before conducting a discussion on would we use a decimal answer in real life versus what would we actually say.  One of the students actually asked when would you use a decimal answer for time but I couldn't think of one.  Even in races they break the time down into minutes, seconds and tenths of seconds but its not in decimal form.

I finally settled on the idea that by calculating a decimal answer, it gives us a better idea of what we need.  For instance, if we are traveling, we  know if its more or less than a certain speed or time.  If we are painting a room, we make sure we order enough supplies but we don't discuss it in terms of decimals.

I'd love to hear from the readership in regard to their thoughts on this particular topic.  Thank you in advance.