Question 1156426
<br>
Tutor @josgartihmetic sets up the problem in the usual way using two variables:<br><pre>
c+p = 15
4c+2.75p = 50<br></pre>
She then suggests solving the problem using substitution.  That is a perfectly good algebraic method; but when the two equations are in this form, elimination is much easier.<br>
Multiply the first equation by 4 and then compare the two equations using subtraction:<br><pre>
   4c + 4p    = 60
   4c + 2.75p = 50
  -----------------
        1.25p = 10
            p = 10/1.25 = 8</pre>
ANSWER: 8 bottles of pop and 15-8=7 bags of chips<br>
If a formal algebraic solution is not required, you can get the answer much faster with a little logical reasoning and mental arithmetic -- and using virtually the same calculations.  It goes like this:<br>
(1) If all 15 items were bags of chips, the cost would be 15 times $4, or $60.  That is $10 more than the actual cost.
(2) Each bottle of pop costs $1.25 less than each bag of chips.
(3) To bring the cost down $10 from $60 to $50, the number of bottles of pop must be $10 divided by $1.25, which is 8.<br>
And again the answer is 8 bottles of pop and 7 bags of chips.<br>