Answer:
80%
Explanation:
"He will start with the Brachiosaurus which has an estimated height of 15 meters and make the model 3 meters on height. by what percent will Ruben decrease the size of the Brachiosaurus in order to fit it into the display"
The percent decrease is the difference in heights divided by the original height.
(15 - 3) / 15
12/15
0.8
So Ruben will decrease the size by 80%.