Teacher2Teacher 
Q&A #18923 
View entire discussion [ next >>]
From: Loyd <Loydlin@aol.com> To: Teacher2Teacher Public Discussion Date: 2010122115:58:55 Subject: Subtraction fractions I liked Ralph's explanation. My experience in teaching algebra students is that this type problem is one that causes problems. I have heard other teachers also say that the teaching of algebra is hampered because many students are weak in fractions. So, I will give another example a little harder. Subtract 5 and 2/3 from 10 and 3/7. Rewrite: 10 3  7 5 2  3 First thing is to get the least common denominator (LCD) which is 21. So we multiply the first fraction by 3/3 and the second fraction by 7/7. The new problems is" 10 9  21 5 14  21  Now we borrow a "whole" as Ralph's said and change it to 21/21 and add that to 9/21 and then we can subtract as usual. The new problem is: 9 30  21 5 14  21 Now they are "like" fractions so we can subtract.  4 16  21 The trick here is that we can always multiply by 1 and not change the value. 3/3 and 7/7 were used as multipliers and both of them are equal to 1. Make sure students can are proficient in finding the LCD and LCM even if denominators are not prime.
Post a reply to this message

[Privacy Policy] [Terms of Use]
Math Forum Home 
The Math Library 
Quick Reference 
Math Forum Search