19 + 44 + 18 + 37=??? With $95.00 in my purse do I have enough money to pay for these groceries? Decide quick! It’s almost my turn in the checkout line! In real life we often have to do calculations quickly in our heads. It can be tough using numbers like the ones listed. We need easier numbers. What are the easiest numbers to add? Often students will say ones or twos.
Today in class we discovered 0 is the easiest number to add. When we want to know about how much something is we can use round numbers (numbers that end in zero) to help us do calculations.
In third grade we teach students how to round to the nearest 10 by making a number line from _1 - _9 with boxes drawn at either end, _5 in the middle, and an arrow under _5 pointing to the right. (Your student should be bringing home the one they made in class today.) Put the number line on the ground and have them straddle it with their heads lined up over the _5. Call out 39. Find the round numbers on either side of 39 (30 and 40). Have them put their heads over 39. Which round number is 39 closer to? (The weight of their heads should be a physical cue pulling them towards 40). Practice with other numbers. Teach that when we have a number like 45 it is right between the round numbers 40 and 50. The rule is to round up.
Now, go back to the original 4 numbers in our problem and round them. Can you quickly tell me if I have enough? Remember, if we see the word "about" in a math problem we don't need an exact amount. Estimate first, then calculate!
Happy rounding!
No comments:
Post a Comment