Answer:
I am not sure if you typed the question correctly, or maybe I misunderstood:
10 credit cards stack is 7,6mm thin.
3 credit cards stack is 2,28 thin.
[tex]\frac{10}{3}[/tex] credit cards stack is [tex]2\frac{8}{15}[/tex] mm thin.
Step-by-step explanation:
0,76mm - single card
10 * 0,76 = 7,6 mm
3 * 0,76 = 2,28 mm
[tex]\frac{10}{3} * 0,76 = \frac{10}{3} * \frac{76}{100} = \frac{760}{300} = 2 \frac{160}{300} = 2 \frac{16}{30} = 2 \frac{8}{15} mm[/tex]