What is b-w?

[Dingdong314]

If 2b-7w=-3 and b=15-2w what is b-w?
I am stuck on this. According to my practice test app, the correct answer is 6. I cannot figure out how to get six? Also, is 7w a negative? Any tips will help.. Thanks!

 

[HallsofIvy]

I'm not sure what you mean by "is 7w a negative?". The "-7w" in "2b- 7w= -3" indicates that you are subtracting 7w from 2b and says nothing about whether or not "7w" is itself a negative number. However, we have two linear equations in b and w so we should be able to determine precisely what b and w are, separately. Since b= 15- 2w, 2b- 7w= 2(15- 2w)- 7w= 30- 4w- 7w= 30- 11w= -3. 11w= 33 so w= 3. Then b= 15- 2(3)= 15- 6= 9. b- w= 9- 3= 6.

 

[Harry_the_cat]

If 2b-7w=-3 and b=15-2w what is b-w?
I am stuck on this. According to my practice test app, the correct answer is 6. I cannot figure out how to get six? Also, is 7w a negative? Any tips will help.. Thanks!

I'm assuming you've just learnt to solve simultaneous equations.

If the question said "If 2b-7w=-3 and b=15-2w find b and w?" would you be able to do it?

Sometimes you have to find "other" things before you can find the final answer.

 

[HallsofIvy]

If b= 15- 2w then 2b= 30- 4w so the first equation is the same as 30- 4w- 7w= -3. Can you solve that for w? And then what is b? Finally, find b- w.

(7w might be either positive or negative depending on what w is. The "-" in 2b- 7w= 3 indicates that 7w is subtracted from 2b.)