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July 3rd, 2016, 10:10 AM   #1
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SAT help!

Hey everyone, I'm having trouble solving these types of problems on Khan academy but can't figure it out.

If 15bx-20>35, where b is a positive constant, which of the following best describes all possible values of 4-3bx?

Last edited by skipjack; September 1st, 2018 at 05:32 PM.
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July 3rd, 2016, 10:18 AM   #2
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Quote:
If 15bx-20>35, where b is a positive constant, which of the following best describes all possible values of 4-3bx?
$15bx-20 > 35$

divide every term by 5 ...

$3bx-4 > 7$

multiply every term by (-1), note that it changes the direction of the inequality ...

$-3bx + 4 < -7$

note $-3bx+4 = 4-3bx$
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July 3rd, 2016, 10:40 AM   #3
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Okay so why do we divide by 5?
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July 3rd, 2016, 10:46 AM   #4
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Okay so why do we divide by 5?
to get the coefficients of the expression (4 - 3bx) that is stated in the question ...
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July 3rd, 2016, 10:47 AM   #5
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Okay thanks makes more sense that way.
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September 1st, 2018, 01:47 AM   #6
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Stress free mind will also grab more information and will store it forever. So if you want to study effectively for your exam, it is suggested that you are having a stress free state of mind. I am indulged in the MBE prep and before studying, I walk a mile with light music on. It really gives me energy to study effectively.

Last edited by skipjack; September 1st, 2018 at 07:22 PM.
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September 1st, 2018, 01:26 PM   #7
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Quote:
Originally Posted by EngineerJay View Post
Hey everyone, I'm having trouble solving these types of problems on Khan academy but can't figure it out.

If 15bx-20>35, where b is a positive constant, which of the following best describes all possible values of 4-3bx?
15bx-20>35, 15bx > 55, 3bx > 11, therefore 4-3bx < -7.

Last edited by mathman; September 2nd, 2018 at 01:18 PM. Reason: correction - arithmetic
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September 1st, 2018, 05:52 PM   #8
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Subtracting 15bx + 35 from both sides of 15bx - 20 > 35 gives -55 > -15bx.

Dividing that by 5 gives -11 > -3bx.

Adding 4 to both sides gives -7 > 4 - 3bx, which is equivalent to 4 - 3bx < -7.
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September 5th, 2018, 12:47 PM   #9
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All points on the line y=4-3bx above the line y=15bx-20

Edit: if you solve for the intersection of the two lines you can express this as for
X<4/(3b)

Last edited by zylo; September 5th, 2018 at 01:20 PM.
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September 5th, 2018, 09:55 PM   #10
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That doesn't make sense, zylo.
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