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### Course: 7th grade>Unit 2

Lesson 3: Percent word problems

# Percent word problem: guavas

We're putting a little algebra to work to find the full price when you know the discount price in this percent word problem. Created by Sal Khan.

## Want to join the conversation?

• When he talks about fractions it confuses me.
(59 votes)
• I definitely agree with you i draged this out because i was forced to
(18 votes)
• what is a Guava?
(41 votes)
• Guavas ae a type of fruit that can be pink or white from the inside. They have a sweet taste and a hard green skin.
(51 votes)
• i did something slightly different that i think is good, but I didn't got the right answer. so if someone could help me, it would be really great. So this is what i did:
-too find the price of each guavas (with 30% off), i divided 12,60 by 6 and i got 2,10\$ each guava with 30% off
-Then i did 30% of 2,10\$, which gave me 0,63. So i add 2,10 with 0,63 which gave me 2,73\$. So each guava WITHOUT 30% off (full price) is equal to 2,73\$.
-Finally i did 2,73% x 2 = 5,46\$ total
BUT i didn't got the right answer and i don't know why!
if someone find my mistake and tell me where it is, i would be really grateful for them!
(20 votes)
• The amount by which the regular price exceeds the sale price is not 30% of the sale price, but instead is 30% of the regular price!

So you can’t just add 30% of \$2.10, to \$2.10, to get a regular price of \$2.73 per guava...this is a very common type of mistake students make with this type of problem.

Instead, you would need to divide \$2.10 by 0.7 to get a regular price of \$3 per guava, since the sale price is 100%-30%=70% of the regular price.
(23 votes)
• let x represent the price of 1 guava fruit.
6x - 6x * 0.30 = 12.60
6x - 1.8x = 12.60
4.2x = 12.60
x = 3
(20 votes)
• Yes, you've done it perfectly. Sal did the same thing, except for the first step. He took x as the price of 6 guava fruits.
(6 votes)
• This was so confusing and no help
(12 votes)
• The first thing that you need to do is to write the equation. So here are the steps:
1.Define the variable x :
x = cost of 6 guavas at full price.
2 We know that today, there is a 30% off on guava. So we subtract:
x - 0.3x
3. It says that the discounted price for 6 guavas is \$12.6.
So we can finish the equation:
1x - 0.30 x = 12.6
Second, we must solve the equation.
1.Simplify. We see that 1x and 0.30 x both have a x. But how to simplify? 1 of something minus 0.30 of something is 0.70 of something. So:
1x- 0.30x = 0.70x.
0.70x = 12.6
2. Get rid of the number on the left-hand side. How? We can divide. But if we divide 0.70 on the left-hand side, we must also divide 0.70 on the right-hand side.
0.70x/0.70 = 12.6/0.70
x = 18.
I hope it helps!
(PS. If you do not know why to divide the same thing on both sides, you can watch the videos about the introduction of equations.)
(16 votes)
• This is confusing, I don't understand percentages world problems. I SO confused.
(12 votes)
• I still don't understand how he got 0.70 by subtracting 0.30 by 1X,I believe my problem is that I didn't understand what 1X was.
(11 votes)
• Look at it this way: The regular price is x. The sale price is 30% off the regular price, so the sale price would be x - 0.3x. Now isolate the variable. The variable x is the same thing as saying 1 times x, or 1x. If you take 30% off 1x, then 70% would remain. This means that the sale price of 6 guavas (\$12.60) is only 70% of the full price, which means that 12.60 = 0.7x. Since 0.7 and x are being multiplied, and we need to find the value of 6, you have to do 12.60 divided by 0.7 to get 18 dollars as the full price, and then you'd have to do 18 / 6 = 3 to get the unit price of each guava. Finally, you do 3 x 2 = 6, so 2 guavas would cost \$6 at the regular price (no tax included).

I hope this helps!
(2 votes)
• whats a guava?
(11 votes)
• A guava is a type of tropical fruit that is pear/avacado-shaped on the outside, but watermelon/cantalope-like on the inside. The inside can either be pink or white. The outside, or rind, is green.
(2 votes)
• It will be much easier for one to understand if it is mentioned that the discount is per each Guava or on 6 of them in total, at the beginning of the video. I was really confused whether it was per guava the discount or on total of them. Then with a little practice on it I found that the difference between per item and on whole is actually 50% no matter what percent of discount it is. (If individually, it will be twice as much as on whole.)
(7 votes)
• If 12.60 is 70% of the sale price, why do we divide 12.60 by 70% to get back to the regular price?

I don't understand, I thought we simply add another 30% bringing it back to 100% sale price.

is timestamp
(5 votes)

## Video transcript

Let's say I go to the fruit store today and they have a sale on guavas. Everything is 30% off. This is for guavas. And it's only today. Only today. So I say, you know what, let me go buy a bunch of guavas. So I go and I buy 6 guavas. So I buy six guavas. And it ends up, when I go to the register, and we're assuming no tax, it's a grocery and I live in a state where they don't tax groceries. So for the 6 guavas, they charge me, I get the 30% off. They charge me \$12.60. \$12.60. So this is the 30% off sale price on 6 guavas. I go home, and then my wife tells me, you know, Sal, can you go get 2 more guavas tomorrow? I say, sure. So the next day I go and I want to buy 2 more guavas. So, 2 guavas. But now the sale is off. There's no more 30%. That was only that first day that I bought the 6. So how much are those two guavas going to cost me? How much are those two guavas going to cost at full price? At full price? So, a good place to start is, to think about how much would those 6 guavas have cost us at full price? This is the sale price, right here? This is the sale price. How much would those have cost me at full price? So let's do a little bit of algebra here. Pick a suitable color for the algebra. Maybe this grey color. So, let's say that x is equal to the cost of 6 guarvas. 6 guavas, at full price. So, essentially, if we take 30% off of this, we should get \$12.60. So let's do that. So if we have the full price of 6 guavas, we're going to take 30% off of that. So that's the same thing as 0.30. Or I could just write 0.3. I could ignore that zero if I like. Actually, let me write it like this. My wife is always bugging me to write zeroes before decimals. So that's the full price of 6 guavas minus 0.30 times the full price of guavas. Some I'm just taking 30% off of the full price, off of the full price. This is how we figure out the sale price. This is going to be equal to that \$12.60 right there. That's going to be equal to \$12.60. I just took 30% off of the full price. And now we just do algebra. We could imagine there's a 1 in front -- you know, x is the same thing as 1x. So 1x minus 0.3x is going to be equal to 0.7x. So we get 0.7x, or we could say 0.70 if you like. Same number. Point, or 0.7x, is equal to 12.60. And once you get used to these problems, you might just skip straight to this step right here. Where you say, 70% of the full price is equal to my sale price, right? I took 30% off. This is 70% of the full price. You might just skip to this step once you get used to these problems in a little bit. And now we just have to solve for x. Divide both sides by 0.7, so you get x is equal to 12.60 divided by 0.7. We could use a calculator, but it's always good to get a little bit of practice dividing decimals. So let's do that. So we get 0.7 goes into 12.60. Let's multiply both of these numbers by 10, which is what we do when we move both of their decimals one to the right. So the 0.7 becomes a 7. Ignore that right there. The 12.60 becomes 126, put the decimal right there. Decimal right there. And we're ready to just do straight up long division. So this is now a 7, not a .7. So 7 goes into 12 1 time. 1 times 7 is 7. 12 minus 7 is 5. Bring down the 6. 7 goes into 56 8 times. 8 times 7 is 56. And then we have no remainder. So it's 18, and there's nothing behind the decimal point. So it;s 18, in our case, \$18. So x is equal to \$18. Remember what x was? x was the full price of 6 guavas. x was the full price of 6. x is the full price of 6 guavas. Now, the question is, how much will 2 guavas cost me at the full price? Well, this is full price of 6. So you immediately could figure out what's the full price of one guava. You divide 18 by 6. So 18 divided by 6 is \$3. That's \$3 per guava at full price. And they're asking us, we want 2 guavas. So 2 guavas is going to be 2 times \$3, so this is going to be \$6. \$6. Another way you could have done it, you could have just said, hey, 6 at full price are going to cost me \$18. 2 is 1/3 of 6. So 1/3 of \$18 is \$6. So, just to give a quick review what we did. We said the sale price on six guavas, \$12.60. That's 30% off the full price. Or you could say this is 70% of the full price. 70% of the full price. And so you could say, 30% -- so if you say x is the full price of 6 guavas, you could say the full price of 6 guavas minus 30% of the full price of 6 guavas is equal to 12.60, and that's equivalent to saying, 70% of the full price is 12.60. You divided -- then we just solved this algebraically. Divide both sides by 0.7, and then we got x, the full price of 6 guavas, is \$18, or that's \$3 per guava or \$6 for 2. Anyway, hopefully you found that helpful.