WEBVTT
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- [Voiceover] Carly tried to
solve an equation step by step.
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And they tell us, they see, we see
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how she tried to solve the equation.
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They say find Carly's mistake.
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So let's see what Carly did.
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She started with 7a = 28.
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Then on the left hand
side she divides it by a
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and on the right hand
side she divides by 7.
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Well this seems strange.
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When you're manipulating an equation
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whatever you do to one
side, you have to do
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to the other side.
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Over here she decides to
divide the left side by a,
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on the right side she
should divide by a as well.
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Or if she wants to divide
the right side by 7,
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she should divide the
left side by 7 as well,
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but she's dividing both sides
by two different things.
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So step 1 is where she makes the mistake.
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The right thing for her to do,
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or I guess maybe the
most reasonable thing,
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if she wants to solve for
a, divide both sides by 7.
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Then she would have
been left with just an a
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on the left hand side,
because it would have been
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7a/7 and a 4 over there.
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She would have said, oh,
a must be equal to 4.
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So let's keep going.
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Let's do a few more of these.
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Trent tried to solve an
equation step by step.
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All right. Find Trent's mistake.
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So a lot of mistakes happening
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in algebra problems right now.
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So g/3 = 4/3.
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Now let's see. The first step.
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g/3 x 3, so he's multiplying
the left hand side times 3
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and on the right hand side,
he's multiplying by 1/3.
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So once again, he's doing
two different things
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to the left and the right hand side
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even though you're supposed
to do the same thing.
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If you do two different
things, the equality
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will not hold anymore.
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Notice, if these two things are...
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If g/3 = 4, if you multiply this times 3
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and you only multiply this times 1/3,
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well then this thing is
going to become larger,
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because is you multiply by
3 that's going to be larger
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if you take the same thing
and multiply it by 1/3.
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Then the equality won't hold true anymore.
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In order for it to hold true,
if you're going to multiply
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the left by 3 you have to
multiply the right by 3.
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So he made a mistake on step 1.
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All right.
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Ling tried to solve an
equation step by step.
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All right. Find Ling's mistake.
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Let's see 12 = p + 6.2.
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All right. So now it looks like,
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on the left hand side Ling adds 6.2
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and on the right hand side, so there was
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p + 6.2 is the old right hand side,
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but it looks they then
try to subtract 6.2.
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So it's the same number, but over here
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they're adding it and over
here they're subtracting it.
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So they're not doing the
same thing to both sides.
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If you want to add 6.2
to the left hand side
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you need to add 6.2 to
the right hand side.
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If you want to subtract 6.2
from the right hand side
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you have to subtract 6.2
from the left hand side.
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So a lot of mistakes going on in step 1.
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Let me see one where there's
not a mistake in step 1.
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All right.
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Alanna tried to solve an
equation step by step.
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4c = 12, divides the left hand side by 4
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and then multiplies the
right hand side by 4.
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No if you're going to divide
the left hand side by 4
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you have to divide the right
hand side by 4 as well.
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You don't multiply it by 4.
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So a mistake in step 1.
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Let's do one more of these.
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All right. n + 12 = 18.3.
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So over here you had n + 12
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and then Rico subtracts 12.
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So if he subtracts 12
from the left hand side
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he needs to subtract 12
from the right hand side.
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It looks like he does that.
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He had 18.3 and he subtracts 12.
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So he subtracts 12 from both sides.
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So the left side is now
n + 12 - 12, was just n,
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which is why he subtracted 12,
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so you're just left with
an n on the left hand side,
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and on the right hand
side, let's see, 18.3 -12.
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Well 18 - 12 is 6, so this should be 6.3.
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So he made a little bit
of an arithmetic mistake
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in step, he made an arithmetic mistake
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and I think we are all done.