$$(31-11)\div2=10.$$ 
Grandma made some cheese dumplings and some blueberry dumplings. Altogether, she made $$31$$ dumplings. If she had made $$11$$ more cheese dumplings, then there would be the same number of blueberry dumplings as cheese dumplings. How many cheese dumplings did grandma make? (2009 Math Kangaroo Problem, Levels 1-2, Question \#19) 
1: $$10$$ 
2: $$21$$ 
3: $$20$$ 
4: $$15$$ 