Math Investigation
Can you hear me now?
PART I :
Me and my family are looking to get cell phones.And we have different plans in different company.My mom only uses phone for emergencies, so 100 minutes a month will be a lot for her. My father uses phone for business a lot, he needs to use 800 minutes a month in business and 50 minutes for personal in one month. And for me, I am a talkative person, I really like to talk to others in phone, so 1800 minutes one month is enough for my "talkative" mouth.
We select three company to choose our plan, Which is China Mobile, China Telecom and China Unicom.
First one is China Mobile: It is selling cards, which costï¿¥35 for 300 minutes, and if you run out of minutes, you have to buy anotherï¿¥35 card.
The graph as shown above is the plan for buying cards.
It increases constantly and each two lines is between 35.
The equation for plans of China Mobile is
And forï¿¥35, it's domain is 0â¤xâ¤300 Forï¿¥70 it's domain is 300<xâ¤600.
Forï¿¥105, it's domain is 600<xâ¤900 Forï¿¥140 it's domain is 900<xâ¤1200
Forï¿¥175 it's domain is 1200<xâ¤1500 Forï¿¥210 it's domain is 1500<xâ¤1800
For the second company, China Unicom, it has a plan ofï¿¥40 a month for 1000 "Anytime" minutes, but if I run out of 1000 minutes, I need to payï¿¥0.45 per minutes I use. And the last plan is from China Telecom, which has no plan butï¿¥0.25 per minute.
The graph above shows two different equation and situation, first one is when the line reach to 1000 parallel, it is the plan ofï¿¥40 a month for 1000 minutes. But after 1000 minutes it increase withï¿¥0.45 per minute.
So, the equation...