This question is not so difficult just a bit of common sense.

Now, first of all you have to convert 60 feet into inches because the diameter of every circle is expressed in inches.

Remember that 1 foot is 12 inches.

60 feet = 720 inches.

However, 720 is the diameter of the tree, the circumference but we need the radius to compare with the radius of every single inside circle

720/2 = 360 radius of the entire trunk.

Now, every single circle has a distance of 30 diameters OR 15 radii

360/15 = 24

The answer is B

Thank you so much..

Thats an excellent approach.

I did a have a different approach, plz let me know if it works

As per the diag. below

Let consider the inner most circle as A

Now the diameter of the circle is = 30 inch

It is given there is a gap of 15 inch between 2 concentric circles, hence the diameter of the next bigger circle i.e B will increase the diameter by 30 inch, and it goes all the way till it matches with the last circle having the diameter of = 60 feet = 720 inches.

Hence the total number of circles formed = \(\frac{720}{30}\) = 24

Therefore the age of the tree was = 24 yrs

Great explanation

Regards

Interesting question!

Princeton Review ques - not GRE official.ref.