5 ways how to say no politely

We all have at least this one 'freind' that we want to avoid. Even though we clearly show them that we do not wat to hang out with them, they just do not get it. But still we want to say NO to lounch or cinema with them without offending them. Here is how to deal with the situation politely and easily. 

1. "I'm sorry. I'm swamped with homework and i have to study for my math test." 
2. ''I'm sorry. I have to help my mother with preperations for her outdoors party she's thowing this weekend.''
3. ''I'm sorry. I have to go to my grandpa's house this weekend.''
4. ''I'm sorry. I feel really dizzy and i think i'll be sick, it may be food poisoning.''
5. ''I'm sorry. I promised my parents that we'll to the seaside together this weekend.'' 

They'll hopefully understand.