Question

Shelly sells ice cream bars at the beach. In addition to a fixed salary, she earns a commission for each ice cream bar she sells. The table shows Shelly's total earnings, y, from selling x bars of ice cream:
Which equation best shows the relationship between x and y?



Ice Cream Sales and Earnings
Number of Bars Sold(x) Total Earnings(dollars) (y)




0 60


1 65

2 70

3 75



y=x+70
y=5x+60
y+5x+70
y+x+60

Answer 1

Given:
x = number of bars sold
y = total earning

x   y
0  60
1  65
2  70
3  75

Total Earnings = Fixed Salary + Commission * No. of Bars sold

y = 5x + 60

Fixed Salary is $60 because even though Shelly did not sell any ice cream bar, she still earned $60.

Commission on every bar sold is $5.

(65 - 60)/1 = 5
(70 - 60)/2 = 5
(75 - 60)/3 = 5

Answer 2

Simply, the question wants you to write an equation for the points they gave you.

The points are:
(0,60)
(1,65)
(2,70)
(3,75)

The first thing we need to do is to find the slope.

$\sf{Slope =\frac{y_2-y_1}{x_2-x_1} =\frac{65-60}{1-0} =\frac{5}{1} =\boxed{\bf{5}}$

The slope is 5.

If we write an equation in the form of y = mx + b, where m is the slope, and b is the y-intercept, we would have so far:

y = 5x + b

Now, we need to find the y-intercept.
We are given the point (0,60)
That point lies on the y-axis, and therefore, 60 is the y-intercept.

Our final equation is y = 5x + 60.