16. Generally speaking, the crossing calculation of 16 can be done in one minute of grade three. The most important thing is to be correct, the second is to let children understand methods and reasoning, and finally the sooner the better.

The Secret of Pupils' Oral Calculations (Multiplication)

1. Multiply the high bits first. Here, multiply the ten digits up and down, as shown in the following figure:

2. Then add the products obtained by cross multiplication of single digits and ten digits, as shown in the figure:

3. Then add up the numbers on each bit, which is the low operation after the high bit ends.

4. The final result can be checked again by other methods to see if the result is accurate.