The digit in the unit position of the integer 1! + 2! +3! + ….+121!Select an answerA3B4C5D6
Question
The digit in the unit position of the integer 1! + 2! +3! + ….+121!
Select an answer
A. 3
B. 4
C. 5
D. 6
Solution
The factorial of any number greater than 4 ends in 0. This is because the factorial operation involves multiplying the number by all positive integers less than it. Once you reach 5, you're multiplying by a number that has a factor of 5 and a factor of 2, which gives a product ending in 0. Any further multiplication will still end in 0.
So, we only need to consider the factorials of 1, 2, 3, and 4.
1! = 1 2! = 2 3! = 6 4! = 24
Adding these up, we get 1 + 2 + 6 + 24 = 33.
So, the digit in the unit position of the integer 1! + 2! +3! + ….+121! is 3.
Therefore, the answer is A3.
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