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 15bx20>35, where b is a positive constant, which of the following best describes all possible values of 43bx? Last edited by skipjack; September 1st, 2018 at 06:32 PM. 
July 3rd, 2016, 11:18 AM  #2  
Math Team Joined: Jul 2011 From: Texas Posts: 2,817 Thanks: 1460  Quote:
divide every term by 5 ... $3bx4 > 7$ multiply every term by (1), note that it changes the direction of the inequality ... $3bx + 4 < 7$ note $3bx+4 = 43bx$  
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 
Math Team Joined: Jul 2011 From: Texas Posts: 2,817 Thanks: 1460  
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 
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Last edited by skipjack; September 1st, 2018 at 08:22 PM. 
September 1st, 2018, 02:26 PM  #7 
Global Moderator Joined: May 2007 Posts: 6,684 Thanks: 658  15bx20>35, 15bx > 55, 3bx > 11, therefore 43bx < 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: 20,285 Thanks: 1967 
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 
Banned Camp Joined: Mar 2015 From: New Jersey Posts: 1,720 Thanks: 124 
All points on the line y=43bx above the line y=15bx20 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: 20,285 Thanks: 1967 
That doesn't make sense, zylo.
