Math CentralQuandaries & Queries


Question from Jessica:

Hello, I'm having trouble helping my daughter she is in 5th grade and I tell you her math is so much different then the math I learned in school and I been out of school for quite some time so it's a little hard for me.
Anyway her math is very confusing for me they are saying use compatible numbers to find two estimates.
I have no idea what that even mean I tried using Google but still don't get it .
The problem is 12 divided by 478 using compatible numbers to find two estimates.... please help

Hi Jessica,

I also am not sure what is expected here. What I do see is that 478 is just a bit smaller than 4800 and 12 divides 48 so my estimate would be

\[\frac{12}{478} \mbox{ is approximately } \frac{12}{4800} = \frac{1}{40}.\]

Here 12 and 4800 are compatible numbers since the division is easily done mentally. I don't know what other pair of compatible numbers is expected. $\large \frac{1}{40}$ is very close to the exact answer.


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