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### Course: 5th grade > Unit 13

Lesson 1: Writing expressions# Constructing numerical expressions

Sometimes, we don't need to solve an equation right away. Instead, we can use the information in a given word problem to construct a numerical expression that represents the information. Created by Sal Khan.

## Want to join the conversation?

- There are no videos explaining the use of brackets? It can be quite confusing to anyone learning for the first time when they try to solve any problem that includes braces and parenthesis.(49 votes)
- brackets and perentheses are the same thing you just want to do the parentheses before the brackets like the teacher taught you parentheses first.(35 votes)

- ngl who else be looking in the comments when their bored??(33 votes)
- I do the videoes are boring(4 votes)

- I just lost my marbles trying to understand this. Pun intended. :)))) It's easy tho(30 votes)
- addition is an opperation so why did Sal say that he solved the problem without using operations even though he used addition?(13 votes)
- So, he didn't really use the operation. He just wrote down what they were asking for. If he had actually performed the operation, he would have come up with 27, which is a number, not a numerical expression.

Hope this helps.(8 votes)

- im the newest comment ever since 7 yrs ago(12 votes)
- Alan found 4 marbles to add to his 5 marbles currently in his pocket. He then had a competition with his friends and tripled his marbles. Write a numerical expression to model the situation without performing any operations. So let's think about what's going on. So he already had 5 marbles in his pocket. And then he found 4 more marbles to add to that. So we can add the 4 marbles to the 5 marbles. So 4 marbles plus the 5 marbles. So that's what happens after the first sentence. He found 4 marbles to add to his 5 marbles currently in his pocket. He then had a competition with his friends and tripled his marbles. So this is how many marbles he had before tripling. And now he's tripling his marbles. So we want to multiply 3 times the total number of marbles he has now-- times 4 plus 5. So this right over here is the numerical expression that models the situation without performing any operations. We, of course, could then actually calculate this. He has 9 marbles before tripling. And then you multiply it by 3 and he has 27. But this is what they're asking for. They want us to write this expression.(0 votes)

- math is a good subject to learn kade.dean30(10 votes)
- my mom makes me do a unit a day cause she thinks im good at math(8 votes)
- Thats good to know keep up the good work(1 vote)

- who understands this(5 votes)
- Hello, this is helpful thanks.(11 votes)
- His is missing its 'h' it looks is(7 votes)

## Video transcript

Alan found 4 marbles
to add to his 5 marbles currently in his pocket. He then had a competition
with his friends and tripled his marbles. Write a numerical expression
to model the situation without performing
any operations. So let's think about
what's going on. So he already had 5
marbles in his pocket. And then he found 4 more
marbles to add to that. So we can add the 4
marbles to the 5 marbles. So 4 marbles plus the 5 marbles. So that's what happens
after the first sentence. He found 4 marbles to
add to his 5 marbles currently in his pocket. He then had a competition
with his friends and tripled his marbles. So this is how many marbles
he had before tripling. And now he's
tripling his marbles. So we want to multiply 3 times
the total number of marbles he has now-- times 4 plus 5. So this right over here is
the numerical expression that models the situation
without performing any operations. We, of course, could then
actually calculate this. He has 9 marbles
before tripling. And then you multiply
it by 3 and he has 27. But this is what
they're asking for. They want us to write
this expression.