Adding Four Two-Digit Numbers

Students add the first pair and the last pair, then combine the two sums.

Use New Numbers to make another set. Choose Worksheet or Answer Key, then use the worksheet’s Print button.

Teaching Notes

Students add the first pair and the last pair, then combine the two sums.

Before You Begin

Two-digit addition

Teaching Steps for Parents and Teachers

Add the first pair, 12 and 18, to get 30.
Add the last pair, 23 and 17, to get 40.
Add the two sums, 30 and 40, to get 70.
Check that each of the four original numbers was added exactly once.

Worked Examples

12 + 18 + 23 + 17 = 30 + 40 = 70

12 + 18 = 30 and 23 + 17 = 40, so the total is 70.

Answer: 70

Common Mistakes and How to Help

Adding an original addend again

Point to the equation to show that 30 already includes both 12 and 18.

Correcting the answer without explaining why

Point to each pair as it is added so no number is missed or counted twice. Have the student start again at the first incorrect step.

Questions to Check Understanding

Which two numbers were added to make 30? Which two made 40?
What does each number in the worked example represent in the original problem?
Can you use the same method when the numbers change?

Practice Advice

Work through the example together and have the student explain why the answer is 70. Ask the student to explain the first two problems aloud, then solve the next three independently. Review the intermediate steps as well as the final answers. If an error repeats, return to the difficult teaching step before assigning more problems.

Next Practice

Choose New Numbers for more practice with the same conditions. Ask the student to explain the reasoning as well as give the answer.
If the student cannot explain the method independently, use smaller numbers to explore the same relationship first.