Question

suppose that the water level of a river is 34 feet and that it is receding at a rate of 0.5 foot per day. Write an equation for the water level ,L ,after D days . In how any days will the water level be 26 feet

Answer 1

Equation: L= -0.5D+34.

The water level be 26 feet in 16 days.

Step-by-step explanation:

Let us consider the initial level (x=0) of the water is 34 feet. Then its coordinate point can be written as (0,34).

The water is receding at the rate 0.5 feet per day, which given us the information that 0.5 is the slope since it is the rate of change and it is decreasing so it is a negative slope.

⇒m= -0.5.

The line equation is  y = mx+c. Let us rewrite as L= mD+c.

Where L is the level of water(y-axis) and D is the days(x-axis) and c is y-intercept.

⇒L= (-0.5)D+c.

To find y-intercept, substitute (0,34) (the known point from the graph) in the equation. Also, the point in y axis when x=0 is y-intercept.

34=  (-0.5)(0)+c.

c=34.

∴L= (-0.5)D+34.

To find the days when the water achieves level as 26 feet:

26 = (-0.5)D+34.

26-34= (-0.5)D.

-8 =  (-0.5)D.

D= $\frac{-8}{-0.5}$.

D= 16.