Answer
If the sum of the digits is divisible by nine, so is the number.
Add up all of the digits in the number and see if the sum is divisible by 9. If you still can't tell, you can add those digits again to see if the new sum is divisible by 9. You can keep going until you the sum is obviously divisible by 9 or not.
For example, is 486451464 divisible by 9?
Do 4 + 8 + 6 + 4 + 5 + 1 + 4 + 6 + 4 = 42.
Is 42 divisible by 9? Not sure, you can then do:
4 + 2 = 6. Which clearly isn't divisible by 9. So our original number, 486451464, isn't either.
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Puzzle 131
Astrology begins with the letter A, biology with B.
Can you find an 'ology' that begins with a P and another that begins with an L?
After the recent BrainBashers drone racing contest, the four contestants were congratulating each other.
Only one drone had the same race number as the position it finished in. Adrian's drone wasn't painted yellow, or blue. Andy's drone beat Avery's drone, whereas Alex's drone beat the drone with race number #1. The drone painted green (Alex's) finished second, and the drone painted blue had race number #4. The drone that had race number #3 was painted red, and beat the drone that finished third. Avery's drone had race number #1.
Can you work out whose drone finished where, its race number, and the colour it was painted?
Hint
Alex's drone finished second, so where did the red drone finish?
Answer Pos Owner # Colour
1 Adrian #3 red
2 Alex #2 green
3 Andy #4 blue
4 Avery #1 yellow
Reasoning
The four colours were: Blue, Green, Red, Yellow.
The four contestants were: Adrian, Alex, Andy, Avery.
By (4), second place was Green, and owned by Alex.
1
2 Alex green
3
4
By (5), Red beat third place, and since Green was second, Red must have been first (and had race number #3).
1 #3 red
2 Alex green
3
4
By (2), Adrian's drone was Red or Green, but we now know that Alex's drone was Green, so Adrian's drone was Red.
1 Adrian #3 red
2 Alex green
3
4
By (3), Andy beat Avery, so they were third and fourth respectively.
1 Adrian #3 red
2 Alex green
3 Andy
4 Avery
By (6), Avery's drone had race number #1.
1 Adrian #3 red
2 Alex green
3 Andy
4 Avery #1
By (1), second place must have had race number #2 (as first place had race number #3, and fourth place had race number #1).
1 Adrian #3 red
2 Alex #2 green
3 Andy
4 Avery #1
Which leaves third place with race number #4, and by (4) was Blue.
1 Adrian #3 red
2 Alex #2 green
3 Andy #4 blue
4 Avery #1
Which leaves fourth place as Yellow.
1 Adrian #3 red
2 Alex #2 green
3 Andy #4 blue
4 Avery #1 yellow
