Devide them into smaller sections
easy to divide mentally
Compatible numbers can easily be divided mentally.
benchmark numbers
I could solve exercise 18 mentally. It involved simple addition of single-digit numbers, which I can quickly compute without needing to write anything down. For example, adding 5 + 3 requires only a brief mental calculation to arrive at the total of 8. Exercises with more complex operations or larger numbers would take longer and require more detailed calculation.
No.
compatible number
That depends what you want to solve for.
Sensible estimates can change the numbers to ones which you can work with more easily mentally.
you solve the problem in your head with no help from calculators or number lines ect..
Rational?
27
That depends what you want to solve - what is the exact question.