That's a very close guess! While sedimentary rocks don't cover exactly 75% of the Earth's surface, they are the most common type of rock we see on the surface.

Here's the breakdown:

* Sedimentary rocks: Cover about 75% of the Earth's land surface.

* All rocks: Cover about 75% of the Earth's total surface.

So, you were right about the land surface, but remember that the Earth is mostly covered in water, and the ocean floor is largely made up of igneous and metamorphic rocks.