This problem was asked to 3rd graders (8 year olds) in Vietnam. Can you figure it out? Place the numbers 1 to 9, using each number once, to make a valid equation. In this video I explain how you can solve this problem logically.\r<br>\r<br>UPDATE: Ive posted all 136 solutions, at the end of this description, found by testing every possibility. What that means is I used a spreadsheet to list out all 9! = 362,880 possibilities, evaluated each expression, and then found out which ones equaled 66.\r<br>\r<br>Sources\r<br>VN Express (Vietnamese) \r<br> \r<br>Via The Guardian (Alex Bellos) \r<br>\r<br>Connect on social media\r<br>My Blog: \r<br>Twitter: \r<br>Books: \r<br>Facebook: \r<br>Google+: \r<br>Pinterest: \r<br>Tumblr: \r<br>Instagram: \r<br>Patreon: \r<br>\r<br>Newsletter (sent about 2 times a year): \r<br>\r<br>The Joy of Game Theory shows how you can use math to out-think your competition. (rated 4/5 stars on 23 reviews) \r<br>\r<br>Math Puzzles Volume 1 features classic brain teasers and riddles with complete solutions for problems in counting, geometry, probability, and game theory. Volume 1 is rated 4.5/5 stars on 11 reviews. \r<br>\r<br>**FULL LIST OF ANSWERS**\r<br>\r<br>The numbers are to be placed in the grid from left to right. For example, the first set of numbers\r<br>\r<br>1 2 6 4 7 8 3 5 9\r<br>\r<br>means\r<br>\r<br>1+13*2/6+4+12*7-8-11+3*5/9-10 = 66\r<br>\r<br>So here are all 136 solutions. As stated in the video, each answer can really be written in 4 different ways when you exchange the first two numbers added or the last two numbers being multiplied. So what we have is 34 distinct equations that can be written in 4 equivalent ways.\r<br>\r<br>1 2 6 4 7 8 3 5 9\r<br>1 2 6 4 7 8 5 3 9\r<br>1 3 2 9 5 6 4 7 8\r<br>1 3 2 9 5 6 7 4 8\r<br>1 3 2 4 5 8 7 9 6\r<br>1 3 2 4 5 8 9 7 6\r<br>1 3 4 7 6 5 9 2 8\r<br>1 3 4 7 6 5 2 9 8\r<br>1 3 6 2 7 9 4 5 8\r<br>1 3 6 2 7 9 5 4 8\r<br>1 3 9 4 7 8 5 2 6\r<br>1 3 9 4 7 8 2 5 6\r<br>1 4 8 2 7 9 5 3 6\r<br>1 4 8 2 7 9 3 5 6\r<br>1 5 2 8 4 7 9 3 6\r<br>1 5 2 8 4 7 3 9 6\r<br>1 5 2 3 4 8 7 9 6\r<br>1 5 2 3 4 8 9 7 6\r<br>1 5 3 9 4 2 7 8 6\r<br>1 5 3 9 4 2 8 7 6\r<br>1 8 3 7 4 5 2 6 9\r<br>1 8 3 7 4 5 6 2 9\r<br>1 9 6 4 5 8 7 3 2\r<br>1 9 6 4 5 8 3 7 2\r<br>1 9 6 7 5 2 4 3 8\r<br>1 9 6 7 5 2 3 4 8\r<br>2 1 4 3 7 9 5 6 8\r<br>2 1 4 3 7 9 6 5 8\r<br>2 3 6 1 7 9 4 5 8\r<br>2 3 6 1 7 9 5 4 8\r<br>2 4 8 1 7 9 3 5 6\r<br>2 4 8 1 7 9 5 3 6\r<br>2 6 9 8 5 1 4 7 3\r<br>2 6 9 8 5 1 7 4 3\r<br>2 8 6 9 4 1 5 7 3\r<br>2 8 6 9 4 1 7 5 3\r<br>2 9 6 3 5 1 7 4 8\r<br>2 9 6 3 5 1 4 7 8\r<br>3 1 4 2 7 9 5 6 8\r<br>3 1 4 2 7 9 6 5 8\r<br>3 2 8 6 5 1 9 7 4\r<br>3 2 8 6 5 1 7 9 4\r<br>3 2 1 5 4 7 8 9 6\r<br>3 2 1 5 4 7 9 8 6\r<br>3 2 4 8 5 1 7 9 6\r<br>3 2 4 8 5 1 9 7 6\r<br>3 5 2 1 4 8 7 9 6\r<br>3 5 2 1 4 8 9 7 6\r<br>3 6 4 9 5 8 7 1 2\r<br>3 6 4 9 5 8 1 7 2\r<br>3 9 2 8 1 5 7 6 4\r<br>3 9 2 8 1 5 6 7 4\r<br>3 9 6 2 5 1 4 7 8\r<br>3 9 6 2 5 1 7 4 8\r<br>4 2 6 1 7 8 5 3 9\r<br>4 2 6 1 7 8 3 5 9\r<br>4 3 9 1 7 8 2 5 6\r<br>4 3 9 1 7 8 5 2 6\r<br>4 3 2 1 5 8 7 9 6\r<br>4 3 2 1 5 8 9 7 6\r<br>4 9 6 1 5 8 3 7 2\r<br>4 9 6 1 5 8 7 3 2\r<br>5 1 2 9 6 7 3 4 8\r<br>5 1 2 9 6 7 4 3 8\r<br>5 2 1 3 4 7 8 9 6\r<br>5 2 1 3 4 7 9 8 6\r<br>5 3 1 7 2 6 8 9 4\r<br>5 3 1 7 2 6 9 8 4\r<br>5 4 8 9 6 7 1 3 2\r<br>5 4 8 9 6 7 3 1 2\r<br>5 4 1 9 2 7 3 8 6\r<br>5 4 1 9 2 7 8 3 6\r<br>5 7 2 8 3 9 6 1 4\r<br>5 7 2 8 3 9 1 6 4\r<br>5 9 3 6 2 1 7 8 4\r<br>5 9 3 6 2 1 8 7 4\r<br>6 2 8 3 5 1 9 7 4\r<br>6 2 8 3 5 1 7 9 4\r<br>6 3 1 9 2 5 7 8 4\r<br>6 3 1 9 2 5 8 7 4\r<br>6 9 3 5 2 1 7 8 4\r<br>6 9 3 5 2 1 8 7 4\r<br>7 1 4 9 6 5 3 2 8\r<br>7 1 4 9 6 5 2 3 8\r<br>7 2 8 9 6 5 3 1 4\r<br>7 2 8 9 6 5 1 3 4\r<br>7 3 2 8 5 9 6 1 4\r<br>7 3 2 8 5 9 1 6 4\r<br>7 3 4 1 6 5 9 2 8\r<br>7 3 4 1 6 5 2 9 8\r<br>7 3 1 5 2 6 9 8 4\r<br>7 3 1 5 2 6 8 9 4\r<br>7 5 2 8 4 9 1 3 6\r<br>7 5 2 8 4 9 3 1 6\r<br>7 6 4 8 5 9 3 1 2\r<br>7 6 4 8 5 9 1 3 2\r<br>7 8 3 1 4 5 2 6 9\r<br>7 8 3 1 4 5 6 2 9\r<br>7 9 6 1 5 2 3 4 8\r<br>7 9 6 1 5 2 4 3 8\r<br>8 2 4 3 5 1 7 9 6\r<br>8 2 4 3 5 1 9 7 6\r<br>8 3 2 7 5 9 1 6 4\r<br>8 3 2 7 5 9 6 1 4\r<br>8 5 2 1 4 7 9 3 6\r<br>8 5 2 1 4 7 3 9 6\r<br>8 5 2 7 4 9 1 3 6\r<br>8 5 2 7 4 9 3 1 6\r<br>8 6 4 7 5 9 1 3 2\r<br>8 6 4 7 5 9 3 1 2\r<br>8 6 9 2 5 1 4 7 3\r<br>8 6 9 2 5 1 7 4 3\r<br>8 7 2 5 3 9 6 1 4\r<br>8 7 2 5 3 9 1 6 4\r<br>8 9 2 3 1 5 6 7 4\r<br>8 9 2 3 1 5 7 6 4\r<br>9 1 2 5 6 7 3 4 8\r<br>9 1 2 5 6 7 4 3 8\r<br>9 1 4 7 6 5 2 3 8\r<br>9 1 4 7 6 5 3 2 8\r<br>9 2 8 7 6 5 3 1 4\r<br>9 2 8 7 6 5 1 3 4\r<br>9 3 1 6 2 5 7 8 4\r<br>9 3 1 6 2 5 8 7 4\r<br>9 3 2 1 5 6 4 7 8\r<br>9 3 2 1 5 6 7 4 8\r<br>9 4 8 5 6 7 1 3 2\r<br>9 4 8 5 6 7 3 1 2\r<br>9 4 1 5 2 7 8 3 6\r<br>9 4 1 5 2 7 3 8 6\r<br>9 5 3 1 4 2 7 8 6\r<br>9 5 3 1 4 2 8 7 6\r<br>9 6 4 3 5 8 1 7 2\r<br>9 6 4 3 5 8 7 1 2\r<br>9 8 6 2 4 1 5 7 3\r<br>9 8 6 2 4 1 7 5 3
