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# Constructing numerical expressions

Sal solves a word problem by constructing a numerical expression. Created by Sal Khan.

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.