2 Answers

Answer
If the Pennies are from 1983 to Present, then roughly 181 pennies.
If the Pennies are from 1982 and earlier, the roughly 146 pennies.
There can be a couple ways to look at it. We will just consider a normal size US cent.
From 1983 to Present pennies weigh 2.5 grams
1982 and earlier (Modern & Wheat Lincolns) pennies weigh 3.11 grams
The difference is due to the a higher amount of Copper (95%) in earlier pennies. Modern pennies contain very little copper and are about 97% Zinc.
1 pound = 453.59237 grams
Math
453.59/2.5 = 181
453.59/3.1 = 146
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Over 1,000 years ago when the British Penny was first minted, they were made from gold. 240 Pennies weighed one pound, which is why the British Pound came to be known as the Pound. There were 240 Pennies to the Pound until Britains conversion to decimal currency in 1971.

1 pound (weight) is equal to about 453 grams. The current British Penny weighs 3.56 grams, so there about 127 Pennies to the pound (weight). 

Source > http://wiki.answers.com/Q/How_many_pennies_weigh_one_pound

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