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Lesson 2: Strategies for adding within 100

# Strategies for adding 2-digit numbers

Sal goes through multiple strategies for adding 2-digit numbers.

## Want to join the conversation?

• Question:
58+15 is the same as 60+ ?
We can move 2 from 15 to 58
58+15
= 58+(2+13)
=(58+2)+13
=60+13

Logically I understand why we are moving 2 from 15 to 58 but in practice I get confused
somehow, are we breaking 15 because we already know 58+15 = > 60 < + something ?
when will I know when to break the first or second number ? I must be either thinking too little or
too much but this has been bothering me a lot. Thanks.
• Moving the 2 is just a strategy, you can just add (8+5)'s answer and (50+10)'s answer together which gets you the answer. What the video is helping you with, is understanding and making it to a tens number for it to be easier to solve!
• I’m gonna do by making tens
(1 vote)
• I’m gona do a number line and much more
(1 vote)
• Hou do I a number line
(1 vote)
• Simply draw a line using a ruler, add some indents and then numbers to create a number line. If you want to try it with bigger numbers, the number lines would be very precise and would use small increments.

Hope this helps!
(1 vote)
• how do I add two digit numbers.
• You can add two digit number in many different ways. You can use a calculator, you can use mental math, you can also look for more strategies on Khan Academy.

To give you a straight and direct answer, it is mostly a process, you can add two digit numbers easily by putting them in a vertical format easier. Let us try this with the two numbers '24' and 72'

We can first put these into our expression
``  24+ 72———— ``

Now, what we can do here is add the ones place and the tens place first independently.

So, 4 + 2 is 6 and 7 + 2 = 9. What we can do now is take these values and put them below the numbers we added

``  24+ 72————  96``

Now, we have added the two-digit numbers '24' and '72' and have got the answer of 96. If you want to try this with any other numbers, just input them into the expression. It does not matter if you have two numbers, three, or five, it works for all of them. If the numbers, you add also equate to ≤10 (bigger or equal to ten) then you can just carry the tens digit and add it to the next row and keep the ones digit.

Hope this helps!
(1 vote)