These two coins would be referred to as: Indian Head cents. In 1887, there were ~45,224,000 coins minted; in 1888, the US Mint produced ~37,490,000 coins. Therefore, the 1888 coin is worth a bit more because fewer were minted.
Take 2 -
The "TRICK" here is to get the question right . . . it should be stated as
"Why are 1888 pennies worth more than 1887 pennies?"
And the answer? -
Because there is one more penny.
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Assuming you are asking about a 1887 Morgan silver dollar. Circulated coins are valued at $30.00-$40.00.
400.00 dollars
A denomination is needed.
The 1887s US coin in VF-20 list at$275.
Dependent on it's condition, it can be worth from $2.00 to $47.00.
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1887 would make it an Indian head cent, so it didn't feature any president.
40.00
It is worth 1 cent.
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Quite a bit because 1887 was a rare year with only 350,000 minted, so in VG - 8 condition it could be worth up to $65.
1 dollar
If it's corroded, only a cent or two. 1906 is a common date for Indian cents, A worn but uncorroded one would retail for around a dollar so few collectors would be interested in a damaged coin.
Assuming you are asking about a 1887 Morgan silver dollar. Circulated coins are valued at $30.00-$40.00.
1887 is not considered a rare date for Morgan dollars. In MS-62 grade, it is currently worth about $30.00
It is worth $50.