Mr. white ordered pizza for the party. medium pizzas have 8 slices and large pizzas have 10. if there are 13 pizzas and 108 slices, how many medium pizzas are there?

Let x and y be the number of medium and large pizzas respectively. Therefore,
x+y = 13 ------- (1)
8x+10y = 108 ------- (2)
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Solving (1) and (2)

From (1), x = 13 -y

Substituting in (2)

8(13-y)+10y = 108
104 - 8y +10 y =108
2y = 4 => y = 2
And then,
x= 13-y => 13 - 2 = 11

Therefore, there are 11 medium pizzas