bonanova Posted August 12, 2008 Report Share Posted August 12, 2008 Make 21, using only the four basic mathematical operators [+, -, x, /] on the numbers 1, 5, 6 and 7. Quote Link to comment Share on other sites More sharing options...
0 Guest Posted August 12, 2008 Report Share Posted August 12, 2008 How many times can use each operation??? Quote Link to comment Share on other sites More sharing options...
0 unreality Posted August 12, 2008 Report Share Posted August 12, 2008 I take it as if we must use each of the four numbers exactly once, though we can use any of the operators as many times or not at all. Right, bonanova? Quote Link to comment Share on other sites More sharing options...
0 Guest Posted August 12, 2008 Report Share Posted August 12, 2008 Make 21, using only the four basic mathematical operators [+, -, x, /] on the numbers 1, 5, 6 and 7. Been working on it for the last hour solid ( at work ) 6 / (1 - 5/7) Quote Link to comment Share on other sites More sharing options...
0 Prime Posted August 12, 2008 Report Share Posted August 12, 2008 Make 21, using only the four basic mathematical operators [+, -, x, /] on the numbers 1, 5, 6 and 7. How about 1+5+6+7+1+1=21? Or did you mean use each number exactly once and each operator as you pleased? Quote Link to comment Share on other sites More sharing options...
0 unreality Posted August 12, 2008 Report Share Posted August 12, 2008 in that case, 7+7+7 ;D or 7*(1+1+1) or 7*(6-5+1*(7-5)) or anything else ;D See my post #3 Quote Link to comment Share on other sites More sharing options...
0 Prime Posted August 13, 2008 Report Share Posted August 13, 2008 in that case, 7+7+7 ;D or 7*(1+1+1) or 7*(6-5+1*(7-5)) or anything else ;D See my post #3 You are not allowed to use "()" -- only "[]". See the statement of the problem. Quote Link to comment Share on other sites More sharing options...
0 unreality Posted August 13, 2008 Report Share Posted August 13, 2008 You are not allowed to use "()" -- only "[]". See the statement of the problem. the brackets were to enclose what you could use. I assumed you can use as many parenteses as required for the order of operations Quote Link to comment Share on other sites More sharing options...
0 Prime Posted August 13, 2008 Report Share Posted August 13, 2008 Here is one possible way: 5+6+7-1=21 in base 8 system, of course. Quote Link to comment Share on other sites More sharing options...
0 bonanova Posted August 13, 2008 Author Report Share Posted August 13, 2008 Been working on it for the last hour solid ( at work ) 6 / (1 - 5/7) taliesin has it. Nice job. Quote Link to comment Share on other sites More sharing options...
0 Guest Posted August 13, 2008 Report Share Posted August 13, 2008 taliesin has it. Nice job. Thanks Quote Link to comment Share on other sites More sharing options...
0 Prime Posted August 13, 2008 Report Share Posted August 13, 2008 taliesin has it. Nice job. Agree on that. Still, I think, my solution (post 9) is valid too. Quote Link to comment Share on other sites More sharing options...
0 Guest Posted August 13, 2008 Report Share Posted August 13, 2008 Here is one possible way: 5+6+7-1=21 in base 8 system, of course. I think you deserve 10 points for that! Quote Link to comment Share on other sites More sharing options...
0 bonanova Posted August 14, 2008 Author Report Share Posted August 14, 2008 I think you deserve 10 points for that! But 10 octal is just an 8 ... Quote Link to comment Share on other sites More sharing options...
0 Prime Posted August 14, 2008 Report Share Posted August 14, 2008 But 10 octal is just an 8 ... Do you mean, you asked to find decimal 21, not octal!? What are the chances of that? Quote Link to comment Share on other sites More sharing options...
0 Guest Posted August 15, 2008 Report Share Posted August 15, 2008 Ok first off I've never even heard of base 8 system lol. And I didn't know you could use parentheses. If you had said that it would have made it a whole lot easier Bonanova. Quote Link to comment Share on other sites More sharing options...
0 Guest Posted August 15, 2008 Report Share Posted August 15, 2008 15 + 6 Quote Link to comment Share on other sites More sharing options...
0 Prime Posted August 15, 2008 Report Share Posted August 15, 2008 15 + 6 I thought of that. But the tribunal decided that you have to use each number exactly once. And you didn't use "7". Quote Link to comment Share on other sites More sharing options...
0 bonanova Posted August 18, 2008 Author Report Share Posted August 18, 2008 Ok first off I've never even heard of base 8 system lol. And I didn't know you could use parentheses. If you had said that it would have made it a whole lot easier Bonanova. The following statement may or may not be false. The previous statement definitely is false. After you figure that out, note that the OP limits the mathematical operators that you can use to "+,-,*,/." Contrarily, parens are just signposts. Yes, they can affect the calculation, but intrinsically, they're not ops. For example 5+6 = 11 = 5+(6) = (5)+6 = (5) + (6) = (5 + 6) = ((5) + 6) = ... Quote Link to comment Share on other sites More sharing options...
0 Guest Posted August 18, 2008 Report Share Posted August 18, 2008 The following statement may or may not be false. The previous statement definitely is false. After you figure that out, note that the OP limits the mathematical operators that you can use to "+,-,*,/." Contrarily, parens are just signposts. Yes, they can affect the calculation, but intrinsically, they're not ops. For example 5+6 = 11 = 5+(6) = (5)+6 = (5) + (6) = (5 + 6) = ((5) + 6) = ... Also, if you think about it, when you write it on paper, the solution to this problem definitely doesn't require any parentheses. They are just there to help when it is all laid out on one line of a forum post. Quote Link to comment Share on other sites More sharing options...
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bonanova
Make 21, using only the four basic mathematical operators [+, -, x, /] on the numbers 1, 5, 6 and 7.
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