Question 23546
7p+5e = 11.60
5p +3e = 7.60


I recommend the elimination (addition) method.  To eliminate the e variable, the common number between the coefficients is 15 (like an LCD!).  To get a 15 in the first equation, multiply both sides by 3.  To get a -15 in the second equation and make the variable subtract out, multiply the second equation by -5.


3(7p+5e) = 3(11.60)
-5(5p +3e) =-5( 7.60)


21p + 15e = 34.80
-25p -15e = -38.00


Add the two equations together:
-4p = -3.20


Divide both sides by -4:
{{{(-4p)/-4 = (-3.20)/-4}}}
p= $.80


Substitute p into the first equation and solve for e:
7p+5e = 11.60
7(.80) + 5e=11.60
5.60 + 5e = 11.60


Subtract 5.60 from each side:
5.60-5.60 +5e= 11.60-5.60
5e = 6.00


{{{(5e)/5 = 6.00/5}}}
e = $1.20


Check in second equation:
5p+3e= 7.60
5(.80)+3(1.20)= 7.60
4.00 + 3.60 = 7.60
It checks!!


Now, the LAST step in any word problem is to ANSWER THE QUESTION!

Cost of 8 erasers = 8(1.20) =$9.60 (plus tax!!)


R^2 at SCC