Question 534161
We can look at these as (x,y) pairs.
(10,300)
(20,400)
(50,700)
.
We can use two of the pairs to define a straight line and then use the third point to force the line go through the third point.
.
m = slope = change in y / change in x
.
300-400 = -100
20-10 = -10
m = 10
.
y = 10x + b
.
700 = 10(50) +b
b = 700-500 = 200
.
y = 10x + 200
.
That means the total cost for the dinner party is $200 + $10 per person.
.
So, x=100 leads us to forecast the total cost = 200 + 10*100 = $1200
.
Done.