Independent solution

How to solve this Density Normalization question

Setup

Setup

Write the density as cx on its support and determine c from total probability.

1=c02xdx=2c1=c\int_0^2 x\,dx=2c
c=12c=\frac12

Model

Model

Integrate the normalized density to obtain the cumulative probability.

F(q)=0qx2dx=q24F(q)=\int_0^q \frac{x}{2}\,dx=\frac{q^2}{4}

Compute

Compute

Set the CDF equal to 0.80 and take the positive root within the support.

q24=0.80\frac{q^2}{4}=0.80
q=3.2=1.788854382q=\sqrt{3.2}=1.788854382\ldots

Answer

Answer

The percentile rounds to 1.79.

1.79(E)\boxed{1.79\quad\text{(E)}}