5(1/4)-2(1/8)-(1/6)
 First of all I'm going to assume that you mean 5 times (1/4) minus 2 times (1/8) minus (1/6), with no mixed numbers. 
 5* (1/4) - 2(1/8) - (1/6)
 One of the ways to go about solving this problem would be to directly multiply out the terms first, instead of making the denominators of the fractions the same.
 So:
 $${\mathtt{5}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{1}}}{{\mathtt{4}}}}\right) = {\frac{{\mathtt{5}}}{{\mathtt{4}}}}$$
 $${\mathtt{2}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{1}}}{{\mathtt{8}}}}\right) = {\frac{{\mathtt{1}}}{{\mathtt{4}}}}$$
 And  $${\frac{{\mathtt{5}}}{{\mathtt{4}}}}{\mathtt{\,-\,}}{\frac{{\mathtt{1}}}{{\mathtt{4}}}} = {\frac{{\mathtt{4}}}{{\mathtt{4}}}}$$ = 1
 Now 1 is the same as 6/6
 So:   $${\frac{{\mathtt{6}}}{{\mathtt{6}}}}{\mathtt{\,-\,}}{\frac{{\mathtt{1}}}{{\mathtt{6}}}} = {\frac{{\mathtt{5}}}{{\mathtt{6}}}}$$
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