Maths-
General
Easy

Question

# Mark has 100 gift card to buy apps for his smart phone .Each week he buys one new app for 4.99 a) Write an equation that relates the amount left on the card ,y , over time x. b) Make a graph of the function

Hint:

## The correct answer is: plot its graph

### Step by step solution:Let the amount left on the gift card be denoted by y.Let the time (in weeks) be denoted by x.The initial amount on the gift card = \$100Amount spent each week = \$4.99Thus, we can say thatRate of change of amount left in the gift card with respect to time (in weeks), m = - 4.99The value is negative as the amount is decreasing.Initial value, c = 100Using the slope intercept form of an equationy = mx + cWe gety = -4.99x + 100The above equation relates the amount left on the card over timeNext, we construct a table with different values of x and corresponding values of y.Putting x = 0 in the above equation, we will get, y = 100Similarly, putting x = 1, in the above equation, we get y = 95.01Continuing this way, we haveFor x = 2, we get y = 90.02For x = 3, we get y = 85.03For x = 4, we get y = 80.04Making a table of all these points, we have x 0 1 2 3 4 y 100 95.01 90.02 85.03 80.04 Now we plot these points on the graph.This is the required graph.

We can find the tabular values for any points of x and then plot them on the graph. But we usually choose values for which calculating y is easier. This makes plotting the graph simpler. We can also find the values by putting different values of y in the equation to get different values for x. Either way, we need points satisfying the equation to plot its graph.