Kasia has 42 sweets.  She keeps $$13$$ for herself and shares the rest equally between her two friends Maya and Lucie.  Lucie then gives $$\dfrac{2}{7}$$ of her sweets to Joan.  How many sweets does Lucie keep? 
Overseas Competition->Knowledge Point->Word Problem Modules->Solving Problems Involving Fractions and Percentages->Knowing the Base