Word Problem for slope intercept graph equation

[mhester88]

Hi,

I have this word problem that is asking for two different answers, the equation for the data and to calculate the shipping rate. I'm not understanding how to address either of the questions. Will someone please help me with this answer? I was able to figure out that the slope is 0.4, I just am lost on what the equation should be with the c and w, which I'm guessing would help me figure out the cost of a 7lb package.

 

[lev888]

How did you get 0? Rise over run is not 0.

 

[mhester88]

I am so sorry, I meant to write 0.4.

 

[HallsofIvy]

Any (non-vertical) line can be written c= aw+ b for numbers a and b. To determine the equation of a line I need to find a and b. it costs $3.55 to ship a 4 pound package so 3.55= a(4)+ b. It costs $4.35 to ship a 6 pound package so 4.35= a(6)+ b.

We need to solve the two equations 4a+ b= 3.55 and 6a+ b= 4.35 for a and b.
Subtracting the first equation from the second eliminates b: 2a= 0.80 so a= 0.80/2= 0.40 as you have.
Putting a= 0.4 into the first equation, 4(0.4)+ b= 1.6+ b= 3.55 so b= 3.55- 1.60= 1.95.

The cost to ship a package weighing "w" pounds is c= 0.40w+ 1.95.

In particular, the cost to ship a 7 pound package is c= 0.40(7)+ 1.90= 2.80+ 1.95= $4.75.
We could also have argued that a 7 pound package is just one pound heavier than the 6 pound package so cost $0.40 more to ship: $4.35+ $0.40= $4.75.

 

[HallsofIvy]

I want to know how do converting mixed number to decimal can you help me please because I don't get it

This doesn't have anything to do with "slope intercept equation". In the future use the "start thread" button to start your own thread.

A "mixed number" is an integer with a fraction, like \(\displaystyle 2\frac{1}{3}\) or \(\displaystyle 4\frac{3}{5}\).
To convert such a fraction to a decimal, convert the fraction to a decimal by doing the "implied division" then add the integer. For example, 3 divided by 5 is 0.6 and adding 4, we get 4.6. \(\displaystyle 4\frac{3}{5}= 4.6\).
And 1 divided by 3 is 0.33333... (the threes continue infinitely) so \(\displaystyle 2\frac{1}{3}= 2.3333...\).