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my daughters math homework states use teh distributive property to solve. The problem is 90-45 how do you do distributive propertywithout the ( ).

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3 Answers

Hi Machelle. If I understand you correctly, you need to solve the problem 90-45 using the distributive property. Normally we don't use the distributive property to solve these types of problems, but for the purposes of education, sometimes it is helpful for the student to try it out. It can help the students develop an intuitive understanding of the distributive property.

The key is to find a common factor for 90 and 45. 9 is a good choice. You can also use 5 or 45.

90-45

=9•10-9•5

=9(10-5)

=9(5)

=45

Now this isn't easier for me than the direct route of just subtracting 45 from 90, but it can help the student see a useful relationship between the numbers. Try it with 5 or 45 as the factor that gets pulled outside the parentheses.

One version of the distribute property is

ab+ac = a(b+c)

This isn't really an operation so much as a rule that can be applied in either direction. If you have something that looks like the left side, you can rewrite it like the right side. If you have something that looks like the right side, you can rewrite it as the left side. In both cases, you are using the distributive property, though we only usually call going from a(b+c) to ab+ac "distributing" the a.

Feel free to use the comment button if you have further questions about this.

Machelle,

I think Robert explained and showed it very well. I would think, as Robert said, that this is simply to help the students understand the distributive property. Robert's first example would be the best to illustrate to a student in lower grade levels.


=9 x 10 - 9 x 5
This works without the parenthesis because of the order of operations (PEMDAS).

If you had to figure out 53*4= you could use the distributive property by taking 50*4=200 and 3*4=12 and then add the two so it would look like this 200+12= 212.