For every $$4$$ shirts Sally bought, she will buy $$1$$ bag. Each shirt costs $$ $5$$ and each bag cost $$ $10$$. She spent $$ $300$$ altogether. How many shirts did she buy?     Marcus\textquotesingle{} workings were as below:  $ $5+ $10= $15$  Number of groups $= $300\div $15=20$ groups  Shirts bought $=20\times1=20$ shirts  She bought $20$ shirts.     Is Marcus\textquotesingle{} solution correct? If not, how many shirts did Sally buy? Show all your workings. 
Overseas Competition->Knowledge Point->Word Problem Modules->Unitary Method Problems->Applying Multiplication and Division