We are asked to find who saves more each week. To do so, we need to find the constant rate of change for each person and compare the results. We will start with Mi-Ling.

Let's analyze how Mi-Ling's savings change over time.

We can see that Mi-Ling's savings increase by

$ 15

every week. Let's use this information to write a unit rate, which is equal to the constant rate of change.

\frac{Change in savings}{Change in time} = \frac{$ 1 5}{1 week}

We found that the constant rate of change for Mi-Ling's savings is

$ 15

per week. Next, we will consider Daniel's savings. To do so, let's take a look at the following graph.

Recall that if we are given two points that lie on a line, we can calculate the rate of change of the line using the following formula.

Rate of change = \frac{Change in y}{Change in x}

Therefore, to find the rate of change, we will pick any two points on the line.

Now we can calculate the constant rate of change.

\frac{Change in savings}{Change in time} = \frac{$ 2 0 - $ 1 0}{( 2 - 1 ) weeks} = \frac{$ 1 0}{1 week}

We got that the constant rate of change for Daniel's savings is

$ 10

per month. Finally, we will compare the rates of change for Mi-Ling and Daniel.

Mi - Ling $ 15 per week > Daniel $ 10 per week

Note that the constant rate of change for Mi-Ling's savings is greater than it is for Daniel's. This means that Mi-Ling saves more per week.

Exercise

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