Regroup. Find the missing number

Question

5 tens 27 ones = __ tens __ ones

Answer 1

This is a "making change" problem.

 

I like to think of regrouping problems as if they involved money. If you had $27 in 1-dollar bills, how many 10-dollar bills could you get with your $27?

 

$27 (in one dollar bills) = $20 + $7 = 2($10) + $7 = 2 ten-dollar bills plus 7 ones.

 

We then add the 2 ten-dollar bills to our stack of 5 ten-dollar bills that we already have, so:

 

5 + 2 = 7 ten-dollar bills, and we have 7 one-dollar bills left.

 

The mathematical question behind the problem is, how many sets of 10 can we get out of 27 ones?

 

So: how many "tens" and how many "ones" do we now have?

 

This can also be modeled with dimes and pennies.