Addition learning path

Left-to-Right Addition: Add the Parts You Can See

Written arithmetic often starts in the ones column, but mental arithmetic can start with the biggest place value. Keep a running total as you move through the number.

Free lessonLearn at your own pace

The strategy

How it works

Start with the leftmost (largest) place value.
Add the next place value to your running total.
Finish with the ones and check that every part was included.

See it in action

Worked examples

Example 134 + 25

30 + 20 = 50.
Add the ones: 50 + 4 + 5.
50 + 9 = 59.

Answer: 59

Example 2126 + 43

100 + 40 = 140.
Add the tens: 140 + 20 = 160.
Add the ones: 160 + 6 + 3 = 169.

Answer: 169

A quick heads-up

Common mistakes to avoid

Adding ones before tens and losing track of the running total; say each subtotal quietly to yourself.
Forgetting to carry a group of ten; regroup whenever the ones total reaches ten.

Your turn

Check your understanding

Choose an answer to see instant feedback and a short explanation. You can take the quiz again any time.

Question 1 of 3

What is 42 + 35?

Keep the momentum

Try a few practice problems

Choose a comfortable range and work through a short round with the free mental math trainer.

Practice addition