Solve a scale drawing word problem | Geometry | 7th grade | Khan Academy

See how we solve a word problem by using a scale drawing and finding the scale factor.

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[Star-xxhj]

I still don't understand my hw...

[stxrstruck]

LITERALLy makes 0 sense. I swear math makes me wanna cry

[angryskimaskman]

legit sal makes things so simple into a whole giant book

[HoneyBee-exyh]

It's a rectangle, not a square...

[bug]

Thank you so very much Khan! This helped me understand so much!!!! 🙂

[nguyenhoanglinh]

my teacher forced me to watch this in school's computer room without a headphones

[reweesebrahim]

I thought about sth else.
A(a)= 1600 A(d)
A(a)/ A(d)= 1600.
Then, we will substitute by the area for both of them
Lenght. Width/ 3 Width= 1600. Width in bottom will cancel Width in top.
So, Length/3= 1600
Length= 4800 inches= 400 feet.

[ryse]

its a rectangle and you're doing a square

[TedsBeach]

I applaud the mission of Khan Academy and I use it often to tutor students. However this video is confusing. I think Sal should do it over. Let me explain where I think the source of confusion lies.

According to the video, the value for the adjacent side of the rectangle in the drawing, like its length, is said to be equal to 3. Which leads to the conclusion that the shape can only be a square. In fact the value for the adjacent side composes an infinite set of positive numbers, including 3 but not only 3. In other words, its shape is not only a square but is any number of rectangles with a length of 3 inches along the base.


And, importantly, finding the answer does not depend on knowing the value of the adjacent side in the drawing. As it happens, only enough information is given to determine the scale factor, from which the length of the dining room is then calculated. Both the areas and the respective values of the adjacent sides cannot be solved for! (This is demonstrated by the equation for the area of the dining room, in which the terms for the adjacent side cancel out.*)


* let x be the value of the adjacent side in the drawing, and SF the scale factor
Area of Dining Room=3x∙1600
Area of Dining Room=(SF∙3)∙(SF∙x)=SF^2∙3x
∴ SF^2∙3x=3x∙1600


Again, the equation will only solve for the value of the scale factor (√1600=40). Note however that any positive number can be substituted for x. It will then produce as many rectangles as there are positive numbers!


To put it another way, the shape can be a rectangle or a square.

I’m sure Sal could find a clear way to explain this in his own words. He really needs to do so or else he will continue to leave a lot of learners feeling very puzzled by his video.

[craigjasper]

Explanation made way more complicated than it actually is

[aoiokumura]

It is a rectangle not a square. Math makes me want to cry because I don't understand.

[bug]

Hi! I'm trying to do a test for scale drawings and don't understand. Do you think you can help me out? If so thank you so very much!

[nc]

Like I know 40 x 3 is 120 but why is 120 important to the answer

[fifaman]

i didn't understand anything this will not help me in my test

[emanyossef]

Thanks a lot, but l wonder that it's mentioned that the dinning roon is rectangular shaped but you dealed with it as a square!!

[inxiti]

This is the FIRST question/topic on KA that I've had ANY problem with. This is the first time the explanation is really poor. This is disappointing too because it shouldn't be hard but, so far in the curriculum there has bee zero mention of square roots, and when to use them or squares. Students aren't taught what to do by the time they reach this problem.

[bruhmoment]

I still don't understand u messed me up when you were like just imagine this or that so I'm like do just imagine any number