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Question : What is the unit digit of the sum of the first 111 whole numbers?

Option 1: 4

Option 2: 6

Option 3: 5

Option 4: 0


Team Careers360 10th Jan, 2024
Answer (1)
Team Careers360 17th Jan, 2024

Correct Answer: 5


Solution : Given: The unit digit of the sum of the first 111 whole numbers.
The sum of first 111 whole numbers = 0 + 1 + 2 + 3 +.........+ 109 + 110
Using formula of sum of A.P. = $\frac{n}{2}[a+l]$
Where $a$ is the first term, $l$ is the last term of the A.P., and n is the number of terms.
= $\frac{111}{2}(0+110)$
= $55 × 111$
$\therefore$ Unit digit = 5 × 1 = 5
The unit digit of the sum of the first 111 whole numbers is 5.
Hence, the correct answer is 5.

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