Find the percent of the area under the density curve where x is less than 1.

The area under a complete density curve is equal to 1. So, the percent of the total area under a portion of the curve is equal to the area under that part of the curve.
We are looking for the area under the density curve when x < 1.
We can use the area formula for a triangle to find this area:
Area = \frac{1}{2} \times base \times height = \frac{1}{2} \times 1 \times 0.1 = 0.05
So the percent of the area under the density curve where x \lt 1 is 5%.
I found an answer from www.khanacademy.org
Density Curves (video) | Khan Academy
An introduction to density curves for visualizing distributions. ... Imagine that you have a continuous data set (like the quantity of water that ... I understand that the area under the curve is the probability of getting an X in that interval. ... AP® is a registered trademark of the College Board, which has not reviewed this resource.
For more information, see Density Curves (video) | Khan Academy