Question: 2520k is a Perfect Square

Comment on 2520k is a Perfect Square

these videos are lifesavers! thank you so much!

PLZ post question related to this lectures, like you have posted at the end of all previous lectures,
Thank you.
greenlight-admin's picture

I typically place related questions under the video that teaches the necessary properties.
To answer the above video questio,n you need to know about some properties of squares of integers.
So, the video lesson "Squares of Integers" ( is where you'll find related questions.


I do not understand the answer to the question. (2520)(70)=176,400. 176,400 is not a perfect square. What am I missing?

greenlight-admin's picture

But 176,400 IS a perfect square.
176,400 = 420²


I needed to go to bed. I was finding the square of 17,640 which is just under 133. Missed a zero. Thanks,

I solved the question by dividing K=2520/ with each answer choice to find an answer 'k' which a perfect square.

2520/35= Not a perfect square, 2520/105=not a perfect square,2520/140=not a perfect square, 2520/210= not a perfect square

2520/70= 36( A perfect square)
greenlight-admin's picture

That's a perfectly valid strategy - nice work!!
By DIVIDING each answer choice, you're removing all of the terms that are NOT part of a perfect square, leaving only the perfect squares.

This is great for TEST THE ANSWERS. When testing the answers, always start with B or D first. Let's pick B. Plug 70 in for k to get (2520)(70) = 176,400. Hit that luscious square root on your calculator to get a whole number: 420. Really easy as that. Now you should also try answer A just to make sure that that's not the lowest value for k that can give a whole number too. Got the answer in less than 30 seconds.

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