Question 1202500
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The other tutor showed a good typical formal algebraic solution, which is likely what was wanted.<br>
But note that you can get some good mental exercise, and good problem-solving experience, by solving the problem using logical reasoning and simple mental arithmetic.<br>
Here is one way you might solve this problem informally.<br>
If all 30 pizzas were plain, the total cost would have been 30($7) = $210.
The actual total cost was $250, which is $40 more than $210.
The "extra" cost of each deluxe pizza is $9-$7 = $2.
The number of deluxe pizzas needed to make that additional $40 of cost is $40/$2 = 20.<br>
ANSWER: 20 deluxe pizzas; and 30-20 = 10 plain pizzas.<br>
CHECK: 20($9)+10($7) = $180+$70 = $250<br>