Answer:
As per the statement:
Mr. Mendez had 24 cows on his farm.
⇒He had number of cows on his farm = 24 cows.
At an auction, he bought 5 more cows
Change in number of cows = 5
We have to find the percent of change in the number of cows on the farm.

Simplify:

Therefore, the percent of change in the number of cows on the farm (to the nearest tenth) is 20.8%