Mental calculation technique

Example
Mental calculation
Reason

398*4
1600-8=1592
398*4=(400-2)*4
[...]

Quick Table of Multiples
[Multiple of 2]
If the last figure of a number is even, then the number is a multiple of 2.
[Multiple of 3]
If the sum of every figure is a multiple of 3, then the number is a multiple of 3.
(Example)
8262; because 8+2+6+2=18 is a multiple of 3, 8362 is a multiple of [...]

Question: Sam put 18 pencils in 3 equal groups. How many pencils are in each group?
Strategy:
1) UNDERSTAND:
What do you need to know?
You need to know that there are 18 pencils and they are divided into 3 equal groups
2) PLAN:
How can you solve the problem?
You can write a number sentence to solve the problem. Write a [...]

Question: Amy and Judy sold 12 show tickets altogether. Amy sold 2 more tickets than Judy. How many tickets did each girl sell?
Strategy:
1) UNDERSTAND:
What do you need to find?
You need to know that 12 tickets were sold in all. You also need to know that Amy sold 2 more tickets than Judy.
2) PLAN:
How can you [...]