.
They just sold 0.55*200 = 110 t-shirts.
They need to sell 200-110 = 90 more t-shirts.
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There is a bunch of lessons on percentage problems
- Percentage problems
- Percentage word problems (Type 1 problems, Finding the Part)
- Percentage word problems (Type 2 problems, Finding the Rate)
- Percentage word problems (Type 3 problems, Finding the Base)
- More complicated percentage problems
- Problems on percentage that lead to unexpected results
in this site.