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 July 3rd, 2016, 11:10 AM #1 Newbie   Joined: Jul 2016 From: North Carolina Posts: 3 Thanks: 0 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 06:32 PM.
July 3rd, 2016, 11:18 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 $-3bx+4 = 4-3bx$

 July 3rd, 2016, 11:40 AM #3 Newbie   Joined: Jul 2016 From: North Carolina Posts: 3 Thanks: 0 Okay so why do we divide by 5?
July 3rd, 2016, 11:46 AM   #4
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 Originally Posted by EngineerJay Okay so why do we divide by 5?
to get the coefficients of the expression (4 - 3bx) that is stated in the question ...

 July 3rd, 2016, 11:47 AM #5 Newbie   Joined: Jul 2016 From: North Carolina Posts: 3 Thanks: 0 Okay thanks makes more sense that way.
 September 1st, 2018, 02:47 AM #6 Newbie   Joined: Aug 2018 From: usa Posts: 1 Thanks: 0 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 08:22 PM.
September 1st, 2018, 02:26 PM   #7
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Quote:
 Originally Posted by EngineerJay 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 02:18 PM. Reason: correction - arithmetic

 September 1st, 2018, 06:52 PM #8 Global Moderator   Joined: Dec 2006 Posts: 19,882 Thanks: 1835 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.
 September 5th, 2018, 01:47 PM #9 Senior Member   Joined: Mar 2015 From: New Jersey Posts: 1,603 Thanks: 115 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 02:20 PM.
 September 5th, 2018, 10:55 PM #10 Global Moderator   Joined: Dec 2006 Posts: 19,882 Thanks: 1835 That doesn't make sense, zylo.

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