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Cindy prepares burgers with two slices of beef each. A box of beef has $20$ slices. How many burgers can she prepare with all the three and a half box of beef? (Adapted from 2013 Math Kangaroo Problem, Level 3-4, Question \#7) 
Overseas Competition->Knowledge Point->Number Theory Modules->Division without Remainders
There are $3\times20+20\div2=70$ slices of beef. $70\div2=35$ 