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Uncertainty

Compatible numbers are numbers you can divide easily. You can use compatible numbers to estimate quotients.

 

Think of a division fact that is like the numbers you are dividing.

Estimate: 181 5.

Think: 20  5 = 4
200 5 = 40

So,  

181 5 is about 40.

 

Estimating with Compatible Numbers

Estimate: 46 6
Think: What number times 6 has a product close to 46?
8 x 6 = 48

So,  

46  6 is about 8.

 

Find where the quotient begins.

Estimate:

312

5
Try dividing hundreds.

5 < 3 Not enough hundreds
Try dividing tens.
5 > 31 Enough tens

So the quotient begins in the tens place.
Find the first digit of the quotient.
Think: About how many 5s in 31?
5 x 5 = 25
too small
5 x 6 = 30 
31 is between 25 and 35. Try 6.
5 x 7 = 35
too big
Since you are estimating, write zeros for the other digits.

is about 60.

 

If two numbers are compatible, one divides the other evenly.

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