Problem of the Day


A number that is a palindrome reads the same way forwards and backwards. For example, 3113 and 7447 are palindromes. Let n be the product of all 4-digit palindromes. What is the unit’s digit of n?

A. 0
B. 2
C. 4
D. 5
E. 8

Reveal Answer

Answer

A. 0

See the Solution

Solution

There are many 4-digit palindromes including some that start and end in 5, such as 5445 and some that start and end with 2, such as 2882. Multiplying these two numbers together will produce a number that ends in zero. No matter what the product is of all the other palindromes, multiplying it by these two numbers will produce something that ends in zero.


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