$np=10(0.8)=8$ The $80$-th percentile is $\frac{250+260}{2} = 255$. 
The following are the weights (in pounds) of ten people: $100, 115, 135, 140, 180, 197, 230, 250, 260, 270$. Find the $80$-th percentile. 
a) $$115$$ 
b) $$135$$ 
c) $$250$$ 
d) $$260$$ 
e) None of the above 