Example 4. Show that one and only one out of
nn +4, n +8, n +12 and n +16 is divisible by 5.
where n is any positive integers
Answers
Step-by-step explanation:
Consider the positive integer is of the form
5q, 5q+1 ,5q+2 ,5q+3.....
Here
b=5
r=0,1,2,3,4,
Where r=0. =n=5q
Now, n=5q is divisible by 5
n+4=5q+4. {not divisible by 5}
n+8=5q+8. {not divisible by 5}
n+6=5q+6. {not divisible by 5}
n+12=5q+12. {not divisible by 5}
Where r=1, n=5q+1
n=5q+1
n+4=5q+5. {divisible by 5}
n+8=5q+9. {not divisible by 5}
n+6=5q+7 {not divisible by 5}
n+12=5q+13. {not divisible by 5}
Where r=2, n=5q+2
n=5q+2
n+4=5q+6 {not divisible by 5}
n+8=5q+10 {divisible by 5}
n+6=5q+8. {not divisible by 5}
n+12=5q+14 {not divisible by 5}
Where r=3, n=5q+3
n=5q+3
n+4=5q+7. {not divisible by 5}
n+8=5q+11 {not divisible by 5}
n+6=5q+9 {not divisible by 5}
n+12=5q+15. { divisible by 5}
When,
r=4, n=5q+4
n=5q+4
ln+4=5q+8. {not divisible by 5}
n+8=5q+12 {not divisible by 5}
n+6=5q+10. { divisible by 5}
n+12=5q+16. {not divisible by 5}
From 1, 2, 3, 4, 5 Its clear that, one and only one out of n,n+4,n+12,n+6 is divisible by 5
Hence, this is the answer.
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