Show that exactly one of the numbers n, n+2 or n+4 is divisible by 4.
Answers
By Euclid Division Lemma
If a and b are 2 positive integers then
a = bq + r [ Where 0 ≤ r < b ]
If b = 3
a = 3q + r
[ Where 0 ≤ r < 3 ]
r = 0 , 1 , 2
:. Numbers = 3q + 0 , 3q + 1 , 3q + 2
Let ,
n = 3q , 3q + 1 , 3q + 2
⭐ If n = 3q
➡️n = 3q
n is divisible by 3
➡️ n + 2 = 3q + 2
n + 2 = 3(1) + 2 = 5
5 is not divisible by 3
:. n + 2 is not divisible by 3
➡️ n + 4 = 3q + 4
n + 4 = 3(1) + 4 = 7
7 is not divisible by 3
:. n + 4 is not divisible by 3
⭐ If n = 3q + 1
↘️n = 3q + 1
n = 3(1) + 1 = 4
4 is not divisible by 3
:. n is not divisible by 3
↘️n + 2 = 3q + 1 + 2
n + 2 = 3(2) + 3
n + 2 = 3(q + 1)
:. n + 2 is divisible by 3
↘️n + 4 = 3q + 1 + 4 = 3q + 5
n + 4 = 3(1) + 5 = 8
8 is not divisible by 3
:. n + 4 is not divisible by 3
⭐If n = 3q + 2
♦️n = 3q + 2
n = 3(1) + 2 = 5
5 is not divisible by 3
:. n is not divisible by 3
♦️n + 2 = 3q + 2 + 2 = 3q + 4
n + 2 = 3(1) + 4 = 7
7 is not divisible by 3
:. n + 2 is not divisible by 3
♦️ n + 4 = 3q + 2 + 4 = 3q + 6
n + 4 = 3(q + 2)
:. n + 4 is divisible by 3