중1) 유리수의 사칙연산

https://www.youtube.com/watch?v=ajE51UxwUUw 

https://www.youtube.com/watch?v=OG2tNKSPq3Y 

https://www.youtube.com/watch?v=ckNrV30JYus 

https://www.youtube.com/watch?v=8Nk5NNiLtlM 

https://www.youtube.com/watch?v=DKt1JwL-heM 

https://www.youtube.com/watch?v=n7L_NAU9gn0