Which of the following numbers should be added to 5 4 4 + 6 to make the resultant number divisible by 8?
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@Chew-Seong Cheong Sir since you use colors so well in your solution..
Can you help me out with this??
1 0 0 2 + 1 0 1 2 + 1 0 2 2 + 1 0 3 2 + 1 0 4 2
I just wanted to color 1 0 3 2 but this did not happen..Can you please patch up the hole?
5 4 4 + 6 ≡ ( − 3 ) 4 4 + 6 ≡ 3 4 4 + 6 ≡ 9 2 2 + 6 ≡ 1 2 2 + 6 ≡ 1 + 6 ≡ 7 ≡ − 1 ( m o d 8 ) ⟹ 8 ∣ 5 4 4 + 6 + 1 .
Hence, the answer is 1 .
Note that 5 2 ≡ 1 m o d 8
The Congruence can be written as 1 + 6 ≡ m o d 8
∴ the sum is equivalent to 7 Hence 1 should be added
5^(even)gives you last digits as 625 where as 5^(odd) gives you 125.. as 5^44 is even power 625 are the last 3 digits which are needed to check if number is divisble by 8 .remainder is 7 so add 1.
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5 4 4 + 6 ≡ ( 5 4 4 mod ϕ ( 8 ) + 6 ) (mod 8) ≡ ( 5 4 4 mod 4 + 6 ) (mod 8) ≡ ( 5 0 + 6 ) (mod 8) ≡ 7 (mod 8) Since g cd ( 5 , 8 ) = 1 , Euler’s theorem applies. Euler’s totient function ϕ ( 8 ) = 4
⟹ 5 4 4 + 6 + 1 ≡ 0 (mod 8) .