Question 1154156
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Note the problem only says he has $25 TO SPEND; it does not say he has to spend the whole $25.  So he can buy<br>
(a) 5 packages of regular batteries: 5($4.25) = $21.25; or
(b) 4 of regular batteries and 1 of alkaline: 4($4.25)+1($5.50) = $22.50; or
(c) 3 of regular and 2 of alkaline: 3($4.25)+2($5.50) = $23.75; or
(d) 2 of regular and 3 of alkaline: 2($4.25)+3($5.50) = $25<br>
Obviously if he is supposed to spend the whole $25 the last option is the right one....<br>
Also note that if he is supposed to spend the whole $25, there are many ways to get to the answer without formal algebra.<br>
You could, of course, list all the possible combinations of 5 packages and find the one that costs a total of $25.<br>
I solved this mentally three different ways before writing my response.  My first solution went like this:<br>
(1) with prices of $4.25 and $5.50, and a total cost of $25.00, the number of packages at $4.25 can't be an odd number;
(2) so the number of packages of regular batteries must be either 2 or 4;
(3) and trying those two possibilities shows the correct answer is 2 packages of regular an 3 of alkaline.<br>