too hard for this old guy

kennyk38 · #1 $Old$ October 22nd, 2009, 05:16 PM

Using only numbers 1,2,7 & 8, each can be used only once, arrive at the number 37 by using plus, minus, multiplication or division in any order.

Wilmer · #2 $Old$ October 22nd, 2009, 10:16 PM

How sure are you that it actually can be done?

kennyk38 · #3 $Old$ October 22nd, 2009, 11:05 PM

The question was asked of me by my 11 yo grand daughter who got the question in her school homework. Glad I am not going to school now.
Wilmer, thank you for your question.

aidan · #4 $Old$ October 23rd, 2009, 04:02 AM

Quote:

Originally Posted by kennyk38 $View Post$

Using only numbers 1,2,7 & 8, each can be used only once, arrive at the number 37 by using plus, minus, multiplication or division in any order.

One way:
concatenate the numbers
{ $\dfrac{8}{2}-1$ } & 7 = 3&7 = 37

.

Wilmer · #5 $Old$ October 23rd, 2009, 07:19 AM

But that assumes brackets and indirect multiplication by 10
(or division by .1) are allowed.

Other ways are possible if not only +-/* are allowed, like:
FLOOR(2^8 / 7 +1) or CEILING(2^8 / 7 * 1).

Since this is a problem given to an 11 y.o. grand daughter
(I have one of those too, Kenny; turned 11 last month!),
I doubt that anything "complicated" is involved.

I have a feeling that with only +-/* allowed, one of the
4 numbers is a typo; if 1,2,7,9 : 29 + 1 + 7 = 37.
Or if 1,2,7,8 to get 36 (not 37): (8 - 2) * (7 - 1) = 36.
But that assumes brackets allowed.

In other words, I think problem as stated is not possible...

kennyk38 · #6 $Old$ October 25th, 2009, 05:25 PM

Quote:

Originally Posted by aidan $View Post$

One way:
concatenate the numbers
{ $\dfrac{8}{2}-1$ } & 7 = 3&7 = 37

.

Aiden, many thanks for your help. You would be correct with your solution which is much appreciated.

Kenny

kennyk38 · #7 $Old$ October 25th, 2009, 05:26 PM

Quote:

Originally Posted by Wilmer $View Post$

But that assumes brackets and indirect multiplication by 10
(or division by .1) are allowed.

Other ways are possible if not only +-/* are allowed, like:
FLOOR(2^8 / 7 +1) or CEILING(2^8 / 7 * 1).

Since this is a problem given to an 11 y.o. grand daughter
(I have one of those too, Kenny; turned 11 last month!),
I doubt that anything "complicated" is involved.

I have a feeling that with only +-/* allowed, one of the
4 numbers is a typo; if 1,2,7,9 : 29 + 1 + 7 = 37.
Or if 1,2,7,8 to get 36 (not 37): (8 - 2) * (7 - 1) = 36.
But that assumes brackets allowed.

In other words, I think problem as stated is not possible...

Wilmer, I have a solution to the problem, 8 divided by 2 minus 1 =3 and then 37. Many thanks for your input.
Kenny

partyshoes · #8 $Old$ October 30th, 2009, 02:24 PM

Is that OK ... just 3 and 7 makes 37?

kennyk38 · #9 $Old$ October 30th, 2009, 10:17 PM

8 divided by 2 =4 - 1 =3 then do the 37 bit.
Cheers and thanks.

Wilmer · #10 $Old$ October 31st, 2009, 05:28 AM

That involves a multiplication by 10: 3*10+7 = 37.

If that's allowed, then why not split the 8 in half vertically:
that'll give you two 3's, and: 33 + 7 - 2 - 1 = 37