math
 

 math







 

Question by  worker5537 (37)

What are numbers called that are easily used to make mental computations?

For example: If you wanted to know 20 x 21, you'd quickly multiply 20 x 20 in your head and then add one more 20. What is that called?

 
+4

Answer by  gigo (1706)

In germany we call this head backing (Kopfstütze) like the thing that saves your head if you have a car crash.

 
+4

Answer by  esteban (1334)

When you use numbers that are close to the given numbers to estimate an answer, you are using "friendly numbers" they are sometimes called "amicable numbers. "

 
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