What are compatible numbers
What are compatible numbers? Compatible numbers are numbers that look nice or friendly with each other when we do mental calculation to estimate a product, but especially a division
Some examples of compatible numbers when doing division are 400 and 10, 36 and 6, 2400 and 12, and 64 and 8
2400 and 12 are compatible because when doing this division (2400/12), we can quickly divide 24 by 12 to get 2 and put two zeros at the end to get 200
Some examples of compatible numbers when doing multiplication are 200 and 40, 1100 and 40, 25 and 4.
1100 and 40 are compatible because we can quickly do this multiplication by multipling 11 and 4 to get 44 and add three zeros at the end to get 44000
Estimate the following division using compatible numbers
When estimating these numbers, keep in mind that we are not claiming the answer will be exact. we are just looking for a reasonable estimate
When estimating with division, if you decrease the value of one number, you should also decrease the value of the other.
If you increase the value of one number, you should increase the value of the other.
This helps to keep the estimate as close as possible to the exact answer.
232 ÷ 11 , 3421 ÷ 9, and 25889 ÷ 52
Compatible numbers for 232 and 11 are 240 and 12. Notice that both numbers were increased!
24 can be divided by 12 to get 2. Then, add a zero at the end to get 20
Compatible numbers for 3421 and 9 are 3200 and 8.
32 can be divided by 8 to get 4. Then add one zero at the end to get 400
400 is a reasonable estimate. 3321 ÷ 9 = 369 and 369 can be
rounded to the nearest hundred to 400
Compatible numbers for 25889 and 52 are 25000 and 50
When dividing 25000 by 50, the zero next to 50 cancels out with one zero of 25000, so the problem becomes 2500 ÷ 5
25 ÷ 5 = 5. Then, add two zeros at the end and the answer is 500
500 is a reasonable estimate because 25889 ÷ 52 = 497.86 and 497.86 is close to 500
Estimate the following multiplication using compatible numbers
72 × 78 and 288 × 415
When estimating with multiplication, if you decrease a number, you should increase the other and vice versa
Compatible numbers for 72 and 78 are 70 and 80.Note that one number was decreased while the other was increased!
Multiply 7 by 8 and add two zeros at the end to get 5600
Compatible numbers for 288 and 415 are 300 and 400
Multiply 3 by 4 and add four zeros at the end to get 120000.
Now, if I ask the question again, what are compatible numbers, would you be able to answer with confidence?
If not, just study again! So, what are compatible numbers? Just kidding!
Take the quiz below to see how well you understand compatible numbers.

Jul 20, 17 10:41 PM
A water tank is emptied at a constant rate. Initially, 36,000 gallons of water were in the tank. A the end of five hours, 16,000 gallons remained. How
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