A pancake 2 inches in diameter contains 7 g of fat. How many grams of fat are in a pancake 5 inches in diameter?

Answer 1

Use a ratio and keep consistent units. Let x = the unknown

Now let's look at the surface area of the volume since the grams of fat will be directly proportional to the volume of the pancake. Assume unit width since this is linear anyway.

Then,

7 grams/(pi*12) = x grams/(pi*2.52) remember that area = pi*r2

So,

x = (7)(pi*2.52)/pi*12) = 43.75 grams

Looking at it another way, the volume ( of unit width) of a pancake with 2 inch diameter (1 inch radius) is pi*(1)2 = pi

And the volume of a pancake with a 5 inch diameter (2.5 inch radius) = pi*(2.5)2 = 6.25

So, the 5" pancake is 62.5 times the volume. So 7 x 6.25 = 43.75