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# Math problem Watch

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1. You have ten identical open-topped boxes with 10 visually identical coins in each.

In nine of the boxes each of the 10 coins has a mass of 10g.
In one box the 10 coins have masses of only 9g each.

How can you find which box is the odd one out?You have a normal mass measurer with a single pan and a scale. With just one weighing you can identify the box with the lighter coins.

What will you weigh?
2. (Original post by Zenarthra)
You have ten identical open-topped boxes with 10 visually identical coins in each.

In nine of the boxes each of the 10 coins has a mass of 10g.
In one box the 10 coins have masses of only 9g each.

How can you find which box is the odd one out?You have a normal mass measurer with a single pan and a scale. With just one weighing you can identify the box with the lighter coins.

What will you weigh?
You take 1 coin from the first box, 2 from the second, 3 from the third and so on.
and record the total weight
3. (Original post by brianeverit)
You take 1 coin from the first box, 2 from the second, 3 from the third and so on.
and record the total weight
I dont understand O_O?
4. When you say "one weighing" do you mean you can only take one measurement? Is this even possible? Cuz it seems pretty impossible
5. Hope you get lucky first time round. If you don't, make balancing scales with the equipment left and use it to find the odd box against the original box measured. Boom!
6. (Original post by Zenarthra)
I dont understand O_O?
If the coins all weighed 10 gm then the total of the weigjhing would be 550 gm.
Suppose instead it was (550 -k) gm then the box trhat you took k coins from is the one with the lighter coins.
7. (Original post by brianeverit)
If the coins all weighed 10 gm then the total of the weigjhing would be 550 gm.
Suppose instead it was (550 -k) gm then the box trhat you took k coins from is the one with the lighter coins.
Oh -.-
That was so simple *face palm

THanks!
8. (Original post by the_chemist)
When you say "one weighing" do you mean you can only take one measurement? Is this even possible? Cuz it seems pretty impossible
I guess so xD
9. (Original post by Kenan and Kel)
Hope you get lucky first time round. If you don't, make balancing scales with the equipment left and use it to find the odd box against the original box measured. Boom!
LOOL
10. (Original post by Zenarthra)
Oh -.-
That was so simple *face palm

THanks!
I thought you could only take one measurement? Isn't his method taking ten?

EDIT: Or at least, more than one?
11. Isn't it because you can find out how many 9g coins you took out by taking increasing amounts of coins. Therefore, you know what box had the 9g coins.
12. Isn't it because you can find out how many 9g coins you took out by taking increasing amounts of coins. Therefore, you know what box had the 9g coins. You can find out how many 9g coins are taken out because if the 9g was in a different box, a different amount of 9g coins would be taken out and when you measure it would measure a different amount. You can calculate the weight and see how many 9g coins there are and thus what box it was in.
13. If you don't mind it - where did you get this problem?
14. (Original post by the_chemist)
I thought you could only take one measurement? Isn't his method taking ten?

EDIT: Or at least, more than one?
No. It's only one weighing.

Take 1 from the first, 2 from the second etc and weight them all together.

If they were all 10g then the result would be 10(1+2+3+...+10)=550

The actual result will be less by 1, 2, 3...or 10 depending which box held the light coins.
15. (Original post by BabyMaths)
No. It's only one weighing.

Take 1 from the first, 2 from the second etc and weight them all together.

If they were all 10g then the result would be 10(1+2+3+...+10)=550

The actual result will be less by 1, 2, 3...or 10 depending which box held the light coins.
Damn that makes sense. That's pretty smart!
16. (Original post by RoyalBlue7)
If you don't mind it - where did you get this problem?
Oh i got it from here: http://nrich.maths.org/
The problem was aimed at kids O_O
We suck -.- haha
17. (Original post by Zenarthra)
Oh i got it from here: http://nrich.maths.org/
The problem was aimed at kids O_O
We suck -.- haha
Thanks...

No we don't!
18. (Original post by RoyalBlue7)
Thanks...

No we don't!
Oh yeah, not we sorry its I*.
And no probs.

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