Question

What will be the unit's digit in the number N² , if N = 1 + 3 +5+ .. + 35 *​

Answer 1

Answer: 6

Explanation:

1 + 3 + 5 + 7 + 9 = 5

Twice of 5 = 0 (unit digit)

Adding 5 again = 5 (unit digit)

[Unit digit for sum of 1 + 3 + 5 + ... + 29.]

Now, if we observe,

31 + 33 + 35 = 1 + 3 + 5 = 9

So, 5 + 9 = 4

Now, N² = 4² = 6.

More:

Cyclicity of a few numbers:

• 1 - 1
• 2 - 4
• 3 - 4
• 4 - 2
• 5 - 1
• 6 - 1
• 7 - 2
• 8 - 4
• 9 - 2