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If the degree measures of the angles of a convex quadrilateral are in the ratio~$3:4:5:6$, by how many degrees does the measure of the largest angle exceed the measure of the smallest angle? 
Overseas Competition->Knowledge Point->Calculation Modules->Ratios and Proportions
$\dfrac{6}{3+4+5+6}\times360^{\circ}-\dfrac{3}{3+4+5+6}\times360^{\circ}=\dfrac{360}{18}\left( 6-3\right)=20\times3=60^{\circ}$ 