Answer:
50
Step-by-step explanation:
Let x represent the number of pizzas cut into small slices. Then the ratio of small to large slices is ...
[tex]\dfrac{8x}{6(90-x)}=\dfrac{5}{3}\\\\8x=10(90-x)\quad\text{multiply by $6(90-x)$}\\\\18x=900\quad\text{add $10x$}\\\\x=50\quad\text{divide by 18}[/tex]
50 of the 90 pizzas were cut into small slices.
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Check
The 50 pizzas cut into 8 small slices each results in 400 small slices. The 40 pizzas cut into 6 large slices each results in 240 large slices. The ratio of small slices to large slices is 400 : 240 = 5 : 3.
