Jin loves carrots! Yesterday she ate $$\frac{1}{4}$$ of her carrots, and today she ate $$\frac{2}{7}$$ of the number of she ate yesterday. She ate 10 carrots today. Yesterday she have started with  carrots. 
Overseas Competition->Knowledge Point->Word Problem Modules->Solving Problems Involving Fractions and Percentages->Finding the Base
$10\div\dfrac{2}{7}\div\dfrac{1}{4}=140$ 