# Thread: too hard for this old guy

1. ## too hard for this old guy

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.

2. How sure are you that it actually can be done?

3. ## Wilmer

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.

4. Originally Posted by kennyk38
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
{ $\displaystyle \dfrac{8}{2}-1$} & 7 = 3&7 = 37

.

5. 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...

6. ## Thanks

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

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

Kenny

7. Originally Posted by Wilmer
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

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

9. ## Sorry no

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

10. 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