How much food is lost when potatoes are peeled?

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

01 June 2008

Responding to the article about large and small potatoes, Manu Namsikho says: “You propose that buying small potatoes is a better deal [but] that is not always [true]! Picture this; before we eat the potatoes, we peel them. But we know that small bodies have a large surface area to volume ratio than large bodies.

“Assuming the thickness of both peelings to be of equal thickness, one is likely to have a larger surface area of peelings from smaller potatoes than larger ones.  …From your estimation, the difference in volume was only 17cc. This can easily be offset by the above and that's why I won't rush to advise any one to buy small potatoes”.

Manu has point, but let’s see if it is correct. In the previous article, the comparison was between two sets of potatoes (one with three and the other with) costing the same price. The total volume of the three large ones was estimated to be 114 cubic centimetres and that of the four smaller ones was 143cc. The difference is 29cc (not the 17cc stated by Manu).

Suppose now that when peeling, one removes a layer of 2mm from the potatoes. How much volume would be peeled off a small one? To find out, we first work out the surface area and then multiply the result by the thickness of the layer.

Readers still in school will confirm that the formula for the surface area is “four-pi-r-squared”. The diameter was 4cm thus the answer is 50 square cm. Multiplying this by the thickness (2mm = 0.2cm) yields a volume of 10cc per small potato, or 40cc for the four of them. Therefore, after peeling, one is left with only 103cc of food.

For the large potatoes, the diameter was 6cm thus the surface area of the peeling would be 113square cm. This gives a peeled volume of 23cc per potato which leaves only 91cc of food. This is still less than the quantity left by the smaller potatoes.

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Anthony Mugo is concerned about how the Gross Domestic Product is calculated. He says, “What really is taken into account when measuring GDP? I find it hard to believe that our GDP is only Sh1.5 Trillion.

“Take in mind that the market capitalization of listed companies [at the Stock Exchange] is Sh869 billion, add to this the value of the thousands unquoted companies, Govt parastatals, NGOs and SMEs... Surely this can't sum up to a measly Sh1.5 Trillion...”

You’ve got it wrong Anthony. GDP is not the value of our assets but what we produce with them. Think about it this way: you may own a car worth a million shillings, but if you don’t use it commercially to make money, its GDP will be zero (actually negative because you will spend money to maintain it).

Still, that opens the age-old debate regarding tithing: Do you give 10 percent of your wealth or of you income?