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## Class 8 Math (Assamese)

### Course: Class 8 Math (Assamese)>Unit 7

Lesson 1: Percent change word problems

# Percent word problem: magic club

Sal solves percent word problems including percent comparisons and percent of change.

## Want to join the conversation?

• Hi everyone
for example, Dave is 170cm tall, and Dave is 10% taller than mike. The same thing as Mike is 10% shorter than Dave?

Also, what exactly do they mean by Dave is 10% taller than mike. Does it mean he is taller by 10% of Mike’s height or 10% of Dave’s height?
I know it might seem easy but I somehow just can’t get over this question.

Thanks •   In your example, Dave is 10% taller than Mike is the same as Mike * (1 + 10%) = Dave. Mike is 10% shorter than Dave is the same as Dave * (1 - 10%) = Mike. Therefore, the two are different things. In the first example, Dave's height depends on Mike's height. In the second example, Mike's height depends on Dave's height. (If you still have doubts, assign specific numbers to Dave or Mike's height and calculate whether the two statements result in the same heights)

Remember, in percent word problems like the one you just asked, when something is taller or shorter, bigger or smaller than another, the independent variable is always the object after 'than'. So the object before 'than' is calculated from the object after 'than'.

A better way to understand this is to use variables. Let Dave be d and Mike be m, the relationship between d and m in the first statement is d = (1 + 10%) * m.

Hope this helps. Feel free to comment below if you have any more questions.
• Hey guys! This is an easier way to calculate a percent word problem (I learnt it in my Marshall Cavandish book). Let's take the first question Sal solved. That is, in a video game, Val scored 30% fewer than Peeta. Peeta scored 1060 points.

So this is the method:

100% = 1060
1%= 10.6
70%= 10.6*70= 742

Therefore, Val scored 742 points. • How do the goblins equal to 1.2 times the wizards •  20% more than implies you start with 100% and add 20% to this to get 120%. If you just stuck with 20%, that would assume there were 5 times as many wizards as goblins.
• why can't Sal just use fractions? 120%=6/5. I got my answer in 10 seconds for the goblins/wizards problem. A kid I tutor was asking me about this question, but I find it easier to use fractions rather than decimals.

just a tip, no hate... khan academy is great • I have analyzed this problem over and over and i have come up with the different result. I was confused on how u solved the problem because i perceived it the other way. And here is my solution:

220 = 100%
Goblin is 20% + 40% = 60%
Wizard is 40%

FOR THE GOBLINS
percent x base = amount
60% X 220 = amount
0.60 x 220 = 132 Goblins

FOR THE WIZARDS
percent x base = amount
40% x 220 = amount
0.40 x 220 = 88 Wizards

What is the 20% of 220?
percent x base = amount
20% x 220 = amount
0.20 x 220 = 44

What is the 10% of 220?
percent x base = amount
10% x 220 = amount
0.10 x 220 = 22

If Goblins and Wizards were EQUAL:
Divide the 20% of 220 by 2.
Goblins: 132-22 = 110
Wizards: 88+22 = 110

Why is this?
No matter how i analyse, i come up with this one which i believed is reasonable. Please explain why your solution is the correct one. Thank you! • Because when it says there is 20% more goblins than wizards you aren't looking for 20% of 220 more,

you are looking for

20% more than the number of wizards
hence-> goblins=wizards+wizards(0.2)

EDIT

so if you plug in your numbers,
goblins = 60% = 132
wizards = 40% = 88

To find 20% more goblins than wizards you would first have to find 20% of wizards (88) which would be...
-> 20% x 88 = 17.6
20% of 88 more goblins would then equal
->88 + 17.6 = 105.6
(not 132)

Just think about the question if you weren't given the information of 220 total. What would the expression be?

goblins = wizards + 20% of wizards
• I don't quite understand the whole video at all. I've wtached the video many times but I'm still stuck in it. • couldn't we just take 10% of 165 and then subtract it without any extra steps • Because that is not what the word problem is asking. The word problem tells us that 165 is the ending height and we need to calculate the beginning height. The problem also tells us that the ending height is 10% greater than the beginning height which is
``    beginning height + beginning height * 10% = ending height``
10% of the ending height is not the same as 10% of the beginning height.
• i cant figure out how to set up an equation on equivalent expressions with percent problems!a tip or/and example or anything would help.thanks. • at isn't it 148.5 • The word problem tells us that 165 is the ending height and we need to calculate the beginning height. The problem also tells us that the ending height is 10% greater than the beginning height which is
``    beginning height + beginning height * 10% = ending height``
You can re-watch the video to see how Sal arrives at the answer, but lets take a look at what happens when we substitute the answers back into the original equation.
``    beginning height + beginning height * 10% = ending height    148.5 + 148.5 * 0.10 = ending height    148.5 +        14.85 = ending height    163.35               = ending height``
or
``    beginning height + beginning height * 10% = ending height    150 + 150 * 0.10 = ending height    150 +      15.00 = ending height    165              = ending height`` 