Unit digit of 1x3x5x...x999
Question
What is the unit digit in the multiplication of 1 × 3 × 5 × 7 × 9 × ... × 999?
Options
1
3
5
9
Explanation
The expression represents the product of all odd numbers from 1 to 999. The sequence includes the number 5, and every other number in the sequence is odd. When 5 is multiplied by any odd number, the unit digit of the resulting product is always 5. Since there are absolutely no even numbers in the series to produce a unit digit of 0, the final unit digit remains locked at 5.
Answer: (c).
Question details
Year
2025
Paper
CSAT
Question
Q10
Section
Numerical Ability
Sub-topic
Unit Digit & Cyclicity
Type
Number theory
Difficulty
Medium
Source hint
Number theory
Same sub-topic — other years
Unit Digit & Cyclicity has appeared in multiple CSAT papers:
See all questions on Unit Digit & Cyclicity
Browse every tagged question across all years