Sunday, February 18, 2007

NPR Puzzle

The Weekend Edition Sunday puzzle for this week is

Challenge for February 18: The object of this challenge is to develop nine different mathematical expressions that equal eight. You must use the digits 2, 7 and one other. And that other digit must be a one in the first expression, two in the next expression and so on, up to nine. You can use a digit once and only once in each expression.

You may use the four arithmetic symbols: plus, minus, times and divided by, as well as exponents and decimal points. You may use parenthesis as you need them. For example: Using the digits 2, 7 and 1 you can make the expressions 2+7-1= 8.

This week's Challenge is from Robert Waynewright in New Rochelle, N.Y.

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I'm currently stuck on 2,5,7, and 2,7,7.

15 comments:

Anonymous said...

Me too. When I went looking for blog comments, I kind of figured that this is what I'd find. The others are relatively easy; there is some complexity in these last too.

Anonymous said...

Think about dividing decimals.

Anonymous said...

7/.7 - 2

Anonymous said...

.2*5 + 7

Arun said...

Ha, talk of being stuck in a groove.
Anyway, the full set of answers is somewhere else on the site.

Anonymous said...

somewhere else on this site??? im gettin killed on a couple of these!

Anonymous said...

I'm stuck on 2,7,8. Any hints?

Arun said...

2,7,8 - use decimals

Anonymous said...

I have solutions for 0,2,7 (7+2**0) and 2,7,10 (2**(10-7)) but can't get 2,7,8. Any ideas?

Anonymous said...

I'm pretty sure the question asks for numbers from 1-9, 0 not included. DOES ANYBODY KNOW 2,7,8???

Anonymous said...

2,7,8 is a lot simpler than most of you imagine. It's simply 7.2 + .8, or 7.8 + .2.

Anonymous said...

I'm stuck on 4 and 7!!!

Anonymous said...

6...?

Arun said...

OK, I had them under "Excitement of Discovery", but here they are, including 0 (0 is not part of the NPR set).

2^0 + 7
2 + 7 - 1
2/2 + 7
(7 - 3) * 2
2^(7-4)
.5 * 2 + 7
2*7 - 6
7/.7 - 2
7.2 + .8
72/9

Anonymous said...

Thanks. I have [(7+9)/2] for number 9 - I'm not sure how the 'digit' rule is to be interpretted. For 8 I have [7+(.2+.8)].