Who can find an answer different than 7.

[switt775]

I got -7 by starting with a negative number less than -10 (as in -11, -12, -13)
Do I win a prize?

Sadly, no, you just illustrated my point.

Number: -12
Add 10 -12+10 = -2
Double -2 x 2 = -4
Subtract 6 -4 -6 = -10
Subtract original
number: -10 -(-12) = 7

When you subtract a negative, you need to reverse the sign and add it.

So the answer is still 7.

[Wood Borer]

It works for complex numbers too. I tried 2 + j3.

[Wongo]

Of course it does. See Ivan's post below. It doesn't matter what x is, it will cancel out in the end.

Think of a number..............
x

Add Ten..................
x + 10

Double the result.............
[x + 10] x 2

Subtract 6................
([x + 10] x 2) - 6

Divide by 2....................
[([x + 10] x 2) - 6]/2

Take away the first number you thought of.........
([([ x + 10 ] x 2) - 6]/2) - X
.
.
.
=([([ x + 10 ] x 2) - 6]/2) - X

=([2x + 20 - 6]/2) - X

=([x + 10] - 3) - x

=x +7 -x

=7

Waste of time

[Stuart]

Subtract original
number: -10 -(-12) = 7

When you subtract a negative, you need to reverse the sign and add it.

So the answer is still 7.

I'm not going through all the maths to check each step, but this step stood out like a sore thumb

-10 -(-12) = 2 How did you get 7?

(If you make 2 mistakes, they might cancel each other out, and you'll accidently get the correct answer.)

Hmmmmm

[tea lady]

Maybe I'll just stick to "Mo hijacking".

[Wongo]

Simple. Make a mistake. (but only 1. If you make 2 mistakes, they might cancel each other out, and you'll accidently get the correct answer.)

Stuart, that was the 2nd mistake he was talking about.

[Wongo]

Damnit Wongo. Read everything before replying.

[Ashore]

Duh what do you want the answer to be
0 subtract 20
1 subtract 18
2 subtract 16
3 subtract 14
4 subtract 12
5 subtract 10
6 subtract 8
7 subtract 6
8 subtract 4
9 subtract 2

[switt775]

I'm not going through all the maths to check each step, but this step stood out like a sore thumb

-10 -(-12) = 2 How did you get 7?

Hmmmmm

Hmmmmm indeed..... Yes, again illustrating the point well. Two mistakes giving the right answer. I seem to have left out a step (divide by 2), but compensated by not knowing how to subtract two numbers, thus maintaining harmony in the universe...

Here is the original set of instructions, with my (now correct) calculations:

Think of a number.............. -12

Add Ten.................. -12 + 10 = -2

Double the result............. -2 x 2 = -4

Subtract 6................ -4 -6 = -10

Divide by 2.................... -10 / 2 = -5

Take away the first number you thought of......... -5 -(-12) = 7



As Ivan so clearly pointed out, it's impossible to find a number which will give a correct answer other than 7.
Good to see someone is keeping me honest....

[Wongo]

Mo worries switt775.

[jow104]

Wish now I hadnt taken the library book back, lots more mathmatical puzzles.

No woodwork in Oz being done, too hot.

No woodwork in UK being done, too cold

It could have kept us busy for the next few weeks.

[Skew ChiDAMN!!]

As Ivan so clearly pointed out, it's impossible to find a number which will give a correct answer other than 7.

Try it with ∞

[Ashore]

or -10

[switt775]

Try it with ∞

Nice try. But according to Wikipedia (which is published on the Internet, so has to be true) infinity is a concept, not a number.

So it doesn't count.

[Blocklayer]

I'm stuck at the add 10 part