Mental Math with Nines

What is the first step in adding nine to a number using the trick discussed?

• Add 9 directly

• Add 5 twice

• Add 10 and then subtract 1

• Subtract 1 and then add 10

If you have 32 ships and 9 are damaged, how many ships remain using the subtraction trick?

• 21

• 24

• 22

• 23

What is the result of adding nine to 54 using the trick?

• 64

• 63

• 65

• 62

Using the subtraction trick, what is 65 minus 9?

• 54

• 55

• 57

• 56

What is the benefit of using these tricks for adding and subtracting nine?

• It helps in memorizing tables

• It is only useful for large numbers

• It makes calculations slower

• It saves time in mental math