Note that order of operations is suspended for this problem. A answer is:
((1/2*5+7)*6*4/9+8)*3 = 100
A computer algorithm was used to solve this problem. If you were just trying to guess, there are 362880 different permutations to try.
There is solution without bringing in extra mathematical operations like brackets or paranthesis but only with the given operations and given order of operations.The simplication of the solution is also strictly without disobaying the priority levels of operations in mathematics.
Only difficulty here is it is a good exercise to go by trial and error method and try and closing in towards a the solution.
The solution is : 8/1*4+2*3*5/6+7*9=100. It means by PEMDAS or PEDMAS an expression like, ab/c + def/g + hi in algebra , where a,b,c,d,e,f,g,h,i can be any of the the values 1 to 9 without repetetion. As in algebra it can be treated as 3 terms with connector, + summing to 100.
There are 3 terms on the left: 8/1*4 with a connector, + and followed by 2*3*5/6 with another connector, + and followed by 7*9.
Do the simplication operatios by PEMDAS (or PEDMAS) priority :
First term: 8*1/4 = 32.
Second term :2*3*5/6= 5.
Therefore the sum (of the terms by PEDMAS) : 32+5+63=100.
Hope this helps.