Question

Alisha bought a collection of 500 old pennies. She chose 20 pennies from the collection and recorded their dates. Seven pennies had dates earlier than 1980.

What is the best estimate of the percent of pennies in Alisha’s collection that have dates earlier than 1980?

Answer 1

The best estimate would be 35%.

7 out of the 20-coin sample were from before 1980; 7/20 = 35%.

Answer 2

Alisha had a total collection of 500 pennies.

She picked randomly 20 pennies from her collection and got that 7 pennies were made before 1980.

She got (7 out of 20) from her sample, i.e. the probability of getting a penny "having dates before 1980" from the sample would be (7 over 20) or 0.35 or 35%.

Similarly, the best estimate from the total collection would be (35% of 500) or 175 pennies.

Hence, final answer is 35% or 175 pennies.