 # Adding Two-Digit Numbers Given One

Directions: Using the digits 0 to 9 at most one time each, fill in the boxes to make a true equation. ### Hint

How can we ensure that all numbers will be 2-digits?

There are many answers including 27 + 53 = 80. Wrong answers include 76 + 53 = 129 because the sum needs to be two-digits.

Source: Robert Kaplinsky

## Time Twister

Directions: Using the digits 0 to 9, at most one time each, create three different …

1. Christine Roberts

I am thinking that the digits should be changed to include 0-9 in order to have a solution such as 27 + 53 = 80 (sample answer). If you want to use only the digits 1-9, then a different sample answer should be provided such as 26 + 53 = 79.

• You are totally right, Christine. I changed it to 0-9.

• Hi, maybe the directions should say to use any of the numbers between 1-9, some will not be used

• Yeah, that would certainly need to get cleared up while introducing the problem to students.

• 63+27=80

2. Should 5 and 3 be excluded since they are already in the problem?

• 63+27=80

3. My 1st graders came up with a number of solutions. 12 + 53 = 65 , 26 + 53 = 79 , 20 + 53 = 73, 10 + 53 = 63 , and 41 + 53 = 63. Afterwards, the class tried to find the lowest/highest sum.

4. My son (Kindergarten) came up with the following combinations. Avoiding the 30’s was a challenge for him but he did well: 14 + 53 = 67, 27 + 53 = 80, and 26 + 53 = 79. Asking the right questions without leading him on was great for making him think. His “a-ha” moment came when he found 47 + 53 = 100. He said, “I guess it has to be less than 47.”

• He wanted me to add that it took us 6 attempts before we got one correct.

5. 6. 14 +53= 67

7. 8. 12+53=65

9. 30 + 53 = 83

10. 14+53=67

11. 