Math Thread

0<n<=1/6

clearly n cannot be negative. multiply by n on both sides then divide by 6 on both sides.

I don't get it

Like yeah I get this but why am I not just finding the set of numbers where n is greater than or equal to 6

1/(6/36) definitely makes in the inequality true

ya but if you pick a number larger than 6/36 aka 1/6 for n, e.g., 1, the inequality's not satisfied

algebraically u just wanna multiply both sides by n and divide both sides by 6, which gives you

1/6 >= n

but then you also want to think about what makes the original inequality not work, e.g., n <= 0

therefore 0 < n <= 1/6

Yeah my brain stops working after I've been studying for like 3 hours

@electrowizard help :slight_smile:

Not with how to solve the question, but to explain why my brain found my answer instead of the correct one

you correctly found the cutoff point 6/36=1/6,but you have the direction wrong.

the correct answer is n<=6/36 and also n is positive so 0 < n <=1/6

dividing by a positive number changes the direction of <, > because dividing by bigger numbers get you smaller numbers. what you did was basically 1/(1/n) >= 1/6, which is incorrect because you need to flip the direction of the inequality if you do that. you would also need to consider the case where 1/n is negative.

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for example, just consider the question

1/x >= 1/6.

clearly x=6 works.
x = 7 doesnt work because 1/7 < 1/6.
x = 5 works because 1/5 > 1/6.
x = -1 doesnt work because that makes 1/x go negative.

so 0 < x <= 6.

for the question its 1/x >= 1/(6/36) like you thought.

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I feel like this shouldn't have been in the challenge problems section. I tend to overthink anything in the challenge problems section.

if you are familiar with the graph of 1/x it also makes the behavior of the solution set pretty obvious.

https://www.google.com/search?q=graph+1%2Fx

There was a problem on telescoping that was similar

Is this really prealgebra stuff? Am I really doing stuff that 5th graders do?

To become the master, you must first be a student

more like 7th grader unless nerd but yea

I passed this with an A in middle school I guess it just wasn't as rigorous

Not that that is a rigorous problem but some of the other ones

@ewiz @hbotz @KrazyKat

where is my error / if there is no error how do i continue to simplify