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Q&A #522

Teachers' Lounge Discussion: Teaching subtraction

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From: Jeanne

To: Teacher2Teacher Public Discussion
Date: 2000110713:58:41
Subject: Using money to understand

Hello, I haven't been able to come up with a way to draw a picture of the base-10 blocks on this particular type of word processor. But I recently wrote a response to a parent homeschooling her daughter which might give you an idea of what to do. Translation: pennies ---------> units dimes -----------> longs dollar bill -----> flats 10-dollar bill --> 1000 block Let's look at this problem using money. For now let's look at a similar problem using smaller numbers. In terms of money, this problem becomes 500 ------> 5 dollar bills -123 ------> - 1 dollar bill, 2 dimes, 3 pennies ----- -------------------------------------- In order to do this problem your daughter needs to "make change." 500 ------> 4 dollar bills, 10 dimes -123 ------> - 1 dollar bill, 2 dimes, 3 pennies ----- --------------------------------------- Then, 500 ------> 4 dollar bills, 9 dimes, 10 pennies -123 ------> - 1 dollar bill, 2 dimes, 3 pennies ----- --------------------------------------- Now she can do the subtraction. 500 ------> 4 dollar bills, 9 dimes, 10 pennies -123 ------> - 1 dollar bill, 2 dimes, 3 pennies ----- --------------------------------------- 377 <------ 3 dollar bills, 7 dimes, 7 pennies What I can't show here is the notation that goes with the original problem, sorry. Now let's look at your original problem. 4000 ------> 4 10-dollar bills - 1296 ------> 1 10-dollar bill, 2 dollars, 9 dimes, 6 pennies --------------------------------------------------------------------- To do this problem, she needs to make change... 4000 ------> 3 10-dollar bills 10 dollars - 1296 ------> 1 10-dollar bill, 2 dollars, 9 dimes, 6 pennies --------------------------------------------------------------------- 4000 ------> 3 10-dollar bills, 9 dollars, 10 dimes - 1296 ------> 1 10-dollar bill, 2 dollars, 9 dimes, 6 pennies --------------------------------------------------------------------- 4000 ------> 3 10-dollar bills, 9 dollars, 9 dimes, 10 pennies - 1296 ------> 1 10-dollar bill, 2 dollars, 9 dimes, 6 pennies --------------------------------------------------------------------- 2704 <----- 2 10-dollar bills, 7 dollars, 0 dimes, 4 pennies Hope this helps. -Jeanne, for the T2T service Thanks for visiting our on-line community. Visit Teacher2Teacher again at http://mathforum.com/t2t/

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