Find 25 using 6, 25, 9, 8 only

You can only use these numbers once, so not square root or cubed root or anything else.

Good Luck!!

• What other rules are there besides no square root, or cubed root? Can we only use basic + - / * ? – n_plum Apr 12 '17 at 16:50
• Anything. It could even be sine or cosine – Samuel Martin Apr 12 '17 at 16:51
• You can only use the numbers once, so because there is no 2 or 3 you can't do square or cubes, but you can use any other operation. – Samuel Martin Apr 12 '17 at 16:55
• Found it. It's the second number in the list. – Ian MacDonald Apr 12 '17 at 17:04
• To eliminate Ian's solution: does each of the four numbers have to be used exactly once? – Rand al'Thor Apr 12 '17 at 17:11

$25 * (9-8)^6$ ...........................

$25\times\lfloor\log(8+6-9)\rfloor$

or

$25+\lfloor\log\log(8+6-9)\rfloor$

• Also 25 | (9 & 8 & 6). – Ian MacDonald Apr 12 '17 at 17:22

$25^{\left \lfloor log_{9}{6*8} \right \rfloor}$

.

$25^{\left \lfloor log_{8}{6*9} \right \rfloor}$

.

$25^{\left \lfloor log_{6}{\binom{9}{8}} \right \rfloor}$

.

:)

$\left | 25, \Phi, ,\left \{ \Phi \right \}, \left \{ \left \{ \Phi \right \} \right \}, \cdots \right | + \left | 6, \Phi, ,\left \{ \Phi \right \}, \left \{ \left \{ \Phi \right \} \right \}, \cdots \right | + \left | 8, \Phi, ,\left \{ \Phi \right \}, \left \{ \left \{ \Phi \right \} \right \}, \cdots \right | + \left | 9, \Phi, ,\left \{ \Phi \right \}, \left \{ \left \{ \Phi \right \} \right \}, \cdots \right |$

• How did you get that answer? – Samuel Martin Apr 12 '17 at 17:14
• @SamuelMartin: A better question is how can anybody not get the answer. – Name Apr 12 '17 at 17:18
• @Name that's not really an explanation, Samuel is just asking how you thought of this – Beastly Gerbil Apr 12 '17 at 17:32
• IMO once you say "Ah, I'll allow sine and cosine", the whole world of mathematical functions can be thrown at the numbers and nothing can stop you anymore. – greenturtle3141 Apr 12 '17 at 23:05
• @Name can you please explain what's going on in your fourth solution? – greenturtle3141 Apr 12 '17 at 23:05

My answer is to do this which is shown below

25%(6*8*9)

• How does this work? – Samuel Martin Apr 12 '17 at 18:16
• mod means remainder when divided by, the remainder when 25 is divided by 432 is 25 – David Huang Apr 12 '17 at 18:21
• I think % is only denoted as mod in computer science? – greenturtle3141 Apr 12 '17 at 23:06
• Yeah, But I believe its still fine as you still get the ans. – David Huang Apr 12 '17 at 23:57