September 15, 2011- Adding Tens + Ones, Reading A Map/Table

We've been sailing down the coastline of three western states:  Washington, Oregon, and now California.  Since the wind and waves can be formidable along the Pacific coast, we plan our journey from port to port.  We can usually travel between 50 and 70 nautical miles (nm) in a day, that is, arriving in a port before dark.  For longer passages, we sail non-stop through the night, taking turns sleeping or being on watch.

With a map and a table of distances, one can plan a trip and estimate how long the trip will take.

Busy Brains love to do math!

Adding Tens:

Adding tens (decade numbers) is easy.  For example, if you know the "partners" of  7, then you can easily figure out the partners of 70, just by adding a 0.  Look:

5 + 2 = 7          

50 + 20 = 70 

Try some yourself!

3 + 4 = 7

30 + 40 = ___

3 + 3 = 6

30 + 30 = ___ 

7 + 1 = 8

70 + 10 = ___

Great job!  Can you make up some more tens problems on your own?     

Other mathematicians prefer to "count on" to find the answer.  Here's how you might count on with ones to find the answer to the problem 5 + 2 = ____:

Write the number 5, followed by two dots (to represent two more ones).

5  . .   

  You would say "five", then count on 2 more ones. (Five, six, seven).  The answer is 7.

"Counting on" by tens is nearly the same.  Here's an example, solving the problem 50 + 20 = _____:

Write the number 50, followed by two sticks (to represent tens). 

50 / / 

You would say "fifty", then count on 2 more tens (Fifty, sixty, seventy).  The answer is 70.

Try some more!

40  / / /  (Hint: Say "Forty", then count on three more tens)

30  / / /

20  / / / 

60  / /

Did you get it?  Nice work, mathematician!

Below is a map of a coastline, similar to the ones we have sailed recently.  The table of distances shows how far it is from one point to the next.  Can you read the table?  How far is it from Vido to Seal Point?  Put your finger under the box that says "Vido to Seal Point".  Now move your finger across to the Distance column.  The box says 20 nm.  That means it is 20 nautical miles from Vido to Seal Point.  Try some more:

Find the distances.

Seal Point to Cape Azul is _____ nm.

Cape Azul to Point Pelican is _____ nm.

Point Pelican to Pharoah Head is _____ nm.

Pharoah Head to Maiden's Leap is _____ nm.

Great!  Now practice what you've learned about adding tens to answer these questions:

How far is it from Vido to Cape Azul?  (Hint:  Look at the table.  Add the two numbers.  20 + 40 )

How far is it from Seal Point to Point Pelican?

How far is it from Cape Azul to Pharoah Head?

How far is it from Point Pelican to Maiden's Leap?

Wow!  Nice work, Busy Brains!

Here's a new challenge for you:

Add 3 or more numbers from the table.  For example,  How far is it from Vido to Point Pelican? (Hint:  You have to add 3 tens numbers.  20 + 40 + 30).

Submit your equation to the Busy Brains site.  It will be appear on the next posting!

Here's how to share your answer with other Busy Brains:

1.  First, click on the title of this post.  
2.  Go to the bottom of the post and click on the words "Post a comment".

Come on!  It's easy and fun!  You'll be able to see your answer posted with the other answers on the next Busy Brains posting!