Bunuel wrote:

The stiffness of a diving board is proportional to the cube of its thickness and inversely proportional to the cube of its length. If diving board A is twice as long as diving board B and has 8 times the stiffness of diving board B, what is the ratio of the thickness of diving board A to that of diving board B? (Assume that the diving boards are equal in all respects other than thickness and length.)

A. 2

B. 4

C. 8

D. 16

E. 64

stiffness = thickness^3/ length ^3

given length of A= 2 * length of B

and stiffness of A = 8 * stiffness of B

t hickness^3= stiffness* length ^3

find for both a and b

A thickness^3= stiffness* length ^3/ B thickness^3= stiffness* length ^3

or say thickness (A/B) ^3= 8 SB* 2^3* Lb/ sb* lb

so thickness (A/B)^3= 64

or thickness ( A/B) = 4 IMO B

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