Answer:
The bear is 35 years of old now.
Explanation:
Leon wanted to know the age of the black bear at the zoo.
He is informed that if he adds 10 years to the age of the bear and then doubles it, the bear would be 90 years old.
Let the present age of the bear is x years.
So, according to the above condition we can write
2(x + 10) = 90
⇒ 2x + 20 = 90
⇒ 2x = 70
⇒ x = 35
So, the bear is 35 years of old now. (Answer)