A flea weighs 8 decigrams, and an ant weighs 3 milligrams. How much more does a flea weigh than an ant?

now, a decigram is "deci" one tenth of a gram, 1/10 gram.

whilst a milligram is "milli" one thousandth of a gram, 1/1000 gram

now, the flea is 8 of those decigrams thus is 8 * (1/10) grams

the ant is 3 of those milligrams thus 3 * (1/1000) grams

let's find their difference.

[tex]\bf 8\left( \frac{1}{10} \right)\implies \cfrac{8}{10}\implies \stackrel{decigrams}{\cfrac{4}{5}} \\\\\\ 3\left( \frac{1}{1000} \right)\implies \stackrel{milligrams}{\cfrac{3}{1000}}\\\\ -------------------------------\\\\ \cfrac{4}{5}-\cfrac{3}{1000}\impliedby \textit{our LCD is 1000}\implies \cfrac{(200\cdot 4)-3}{1000}\implies \cfrac{800-3}{1000} \\\\\\ \cfrac{797}{1000}\implies 797\left( \frac{1}{1000} \right)\implies 797~milligrams[/tex]