Question

99 % of the trees in our neighborhood are eucalyptus trees. The town planning commission wants to get rid of some of these trees because they spread too quickly. However, the people in my neighborhood like the trees. The commission argues that their new eucalyptus tree removal plan will cut down so few eucalyptus trees that 98% of the trees in our neighborhood will be eucalyptus trees. If the plan only involves removing eucalyptus trees, what percent of the existing trees in my neighborhood would the plan remove

Answer 1

50%

Explanation:

Let the total number of trees be T and suppose that this is made up of eucalyptus trees E and other kinds of trees, O.

Then E+O=T, and since 99% of the trees are eucalyptus trees, EE+O=0.99.

Therefore

0.99E+0.99O=E

0.01E=0.99O

E=99O.

Suppose we reduce the number of eucalyptus trees by some amount x and that the remaining number of eucalyptus trees are now 98% of the total trees.

Then we would have E−x(E−x)+O=0.98.

Therefore,

0.02(E−x)=0.98O

0.02E−0.02x=0.98O

0.02x=0.02E−0.98O

x=E−50(0.98)O

x=E−49O

x=E−49(E99)

x=5099E≈0.505050...×E.

So we end up removing a little over half of the eucalyptus trees. EDIT: Forgot to mention - removing 50.505050...% of the eucalyptus trees means that we are removing 0.50505050....×0.99T which is 0.5T or half the trees in the neighborhood.