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Constructing integers using 4s
By Michael Latham on Tuesday, September 24, 2002 - 02:50 pm:

Is it possible to create the numbers 13, 14, 18 and 19 by using the number 4, four times only. (plus any signs or symbols you may need) The closest I have got is:

4.4 x 4 + .4 = 18

Any advances? Many thanks

By Lee L on Tuesday, September 24, 2002 - 03:27 pm:

(4-0.4)/0.4+4=13
(4+4×0.4)/0.4=14
( 4 + 4 - .4 )/( .4 ) = 19

By Emma McCaughan on Tuesday, September 24, 2002 - 06:18 pm:

4! (=24) and Ö4 are both useful.

By Ian Short on Tuesday, September 24, 2002 - 09:16 pm:

4!-4-4/4=19
Ö4×Ö4×4 +Ö4=18
Ö4×Ö4×4 -Ö4=14
44/4+Ö4=13

I'm not too sure what the boundaries of this problem are.

By Michael Latham on Wednesday, September 25, 2002 - 09:45 am:

Thanks to all contributors. Believe it or not, this problem was set as homework for a 9 year old .

By Emma McCaughan on Wednesday, September 25, 2002 - 02:22 pm:

Usually when I've set this to 11 year olds, it's been a case of "see how many of the numbers 1-100 you can do"; we've then collated answers, and then there's been a general challenge to anyone to find the last few. I certainly wouldn't worry about every individual finding every one!
There was a nice variant on this problem when I was at school - using the four digits of the year to make the numbers 1-100. It doesn't work too well now, but it was great in the 1980s.