Math task for kids - dare to solve it? :)
 

My son (he is 13 BTW), just asked me to help him with this school math task:

What is a sum of figures (digits) in the result of the simple expression below?
2^2008 * 5^2011

I've solved it with my son already, but will someone here able to solve it? Remember it's a just a homework task for 13 y.o. kids :)

P.S. "^" in that expression is a power sign (to raise a given number to the given power)

Hmm.. 21 views and no single try to solve it? :) C'mon guys, it's just a standard school task for kids, but not something from a high math course!

By sum of figures, I meant the following:
124 = 1+2+3 = 6
10082 = 1+0+0+8+2 = 11
7 = 7 = 7
82637 = 8+2+6+3+7 = 26
etc..

Answer is 8

If I was your son, I'd never ask for your help again :1orglaugh

Just a typo of course :)

The answer is accepted. Anyone else?

I will tell which one is right and will show the calculation if necessary, but just let's wait for more answers. Don't post your calculations please, just the answers. Otherwise it won't be interesting.

zzzzz - the answer is 8.
You can even do it in windows calculator if you're lazy.

The answer is 12500....0000 so 8, come on, not very hard...

this is one crazy pic in your avatar, my eyes hurt to look at it while trying to figure it out lol

nice shop job

It looks tricky, but a quick flashback to grade 6 math, and you get:

2^2008 * 5^2011 = (2^2008)*(5^2008)*(5^3)=125*(10^2008)

:1orglaugh:1orglaugh

Why would we keep it going after the first answer was the right one? :winkwink:

Congrats! This is the only right answer. Windows calculator is not an option, because you have to prove the solution. In a way as woj did above.

:1orglaugh:1orglaugh

As I said, you can *also* do it in calculator. :error

Because after that, the one should be explaining on how he got it. As I said, Windows calc is not a right way to do that (you won't have it on a school's exam) :)

Boring.......

to look for wrong ones

Sorry, I've missed that *also*. Course if you did it manually, your answer is also correct. :thumbsup

Ok, here is another one from a same today's homework.

1*2*3*...*n = 2^15*3^6*5^3*7^2*11*13

What is n there? :winkwink:

1+1+1+1+1+1+1+1= 8 :)

The answer is 42

16 :) ....

Course it's a wrong answer :) BTW, it's ok to post your calculations to show it wasn't solved with a windows calc :)

n = 16 :winkwink:

No it's not...

The answer is always 42...

:thumbsup:thumbsup

:1orglaugh

Still no one is able to prove the answer with formula? :)

We're bored of this already.

We wrote the answer, already. :-P

It's just a matter of expanding the right of the equality and then rewriting it in factorial form.

2^15*3^6*5^3*7^2*11*13=

2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x3x3x3x3x3x3x5x5x5x7x 7x11x13=

2x3x(2x2)x5x(2x3)x7x(2x2x2)x(3x3)x(2x5)x11x(2x2x3) x13x(2x7)x(3x5)x(2x2x2x2)=

2x3x4x5x6x7x8x9x10x11x12x13x14x15x16=

16 factorial=

16x15x14x13x12x11x10x9x8x7x6x5x4x3x2x1=

1x2x3x4x5x6x7x8x9x10x11x12x13x14x15x16

n=16

Q.E.D.

Still... good to see a father taking such an interest in his son's math homework. If more did so, I think we'd be further along a better path.

Very impressive! I know nothing about your math background but it's much above the average webmaster here, because I mentioned the number of topic views but only D gave a right answer to the second task.

Thanks, I'm just to see him growing smart. I believe I do like every other parent.