Dividing by Powers of 10
Date: 09/12/98 at 15:26:50 From: Grace Subject: Dividing by 100, 1000... Dear Dr. Math, My sister (6th grade) can't figure out how to divide by numbers like 100, 1000 and so on. My mom and I just can't figure out how to explain it to her. Please tell me how to explain it to her so that she can understand. Grace Paris, France
Date: 09/14/98 at 09:16:42 From: Doctor Peterson Subject: Re: Dividing by 100, 1000... Hello, Grace. If what I have to say doesn't help, you may need to tell me how you have tried to explain it and what objections she gives, and perhaps also what else she does understand so we can find the best way to relate this new idea to what she knows. Or perhaps she understands it in simple cases but has trouble if there is no decimal point or if extra zeroes have to be added. Assuming your sister is working with decimals, it's very simple: to divide by 10, move the decimal point one place to the left; to divide by a power of 10, move it one place to the left for each zero in the number. For example: 123 / 10 = 12.3 123. - / left one place one zero 12.3 123 / 100 = 1.23 123. -- / left two places two zeroes / 1.23 If she doesn't believe this, she can just do the long division and see how the answer comes out. You could also explain it in terms of place value. If you divide by ten, hundreds become tens, tens become ones, and ones become tenths: 123 = 1 hundred, 2 tens, 3 ones | | | | | | divide by ten v v v 1 ten, 2 ones, 3 tenths = 12.3 Each zero in 100 means one more ten to divide by, so there is one more decimal place to move. Let me know if that helps! - Doctor Peterson, The Math Forum Check out our web site! http://mathforum.org/dr.math/
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