Last updated: October 22, 2026 · Written by the Math Made Easy math teachers
Always state what the slope and intercept mean in the units of the situation.
Standards: 8.SP.A.2, 8.SP.A.3 · Level: Grade 8
Problem 1 Predict with a line ★★★
A model for a trend is y = 3x + 10. Predict y when x = 6.
Problem 2 Plant model ★★★
A plant’s height in centimeters is modeled by y = 2.5x + 12, where x is the number of weeks since it was measured first. Interpret the slope and the y-intercept.
Problem 3 Which line fits? ★★★
The graph shows pages read over eight days and two lines. Which line is the better fit? Explain.
Problem 4 Equation from two points ★★★
A trend line passes through (2, 11) and (6, 23). Write its equation.
Problem 5 Draining pool ★★★
The amount of water in a pool is modeled by y = −4x + 90 gallons, where x is minutes since the drain opened. How much water is left after 7 minutes?
Problem 6 Count the points ★★★
A line y = 2.5x + 2 is drawn on the graph. Count the points above, below, and on the line, and decide whether it is a good fit.
Problem 7 Used car model ★★★
The value of a used car, in thousands of dollars, is modeled by y = −1.7x + 20.6, where x is its age in years. Interpret the slope and the y-intercept.
Problem 8 Equation from a graph ★★★
The trend line passes through (0, 3) and (10, 23). Write the equation of the line.
Problem 9 Predict from the model ★★★
Use the model y = 2x + 3 to predict the sales on day 7.5.
Problem 10 Reach a target ★★★
In the model y = 2x + 3, find x when y = 21.
Problem 11 Prediction error ★★★
The study model is y = 5x + 51. A student who studied 4 hours scored 70. How far is the actual score from the predicted score?
Problem 12 Is the prediction safe? ★★★
The study model y = 5x + 51 is based on data for 1 to 8 hours of study. Predict the score for 3.5 hours and for 20 hours, and say which prediction is reasonable.
Problem 13 Handle the outlier ★★★
A scatter plot has ten points that follow a clear rising line and one point far below the line. Should that one point change where the line of best fit is drawn? Explain.
Problem 14 Equation from a table ★★★
Three points lie on a trend line: (1, 9), (3, 17), and (5, 25). Write the equation, then predict y when x = 12.
Problem 15 Bike rental ★★★
A bike shop’s charges are modeled by y = 14x + 30, where x is the number of hours rented and y is the cost in dollars. Interpret the slope and intercept, then find the cost for 5.5 hours.
Problem 16 Battery life ★★★
A phone battery percentage is modeled by y = −12x + 100, where x is hours of use. Find the charge after 5.5 hours, and the time when the battery reaches 20%. Round to the nearest tenth of an hour.
Problem 17 Candle burning ★★★
A candle’s height is modeled by y = −0.8x + 24 inches, where x is the number of hours it burns. Find the height after 10 hours and the time when it burns out.
Problem 18 Savings plan ★★★
A student’s savings, in dollars, are modeled by y = 12x + 85, where x is the number of weeks. In which week will the savings first reach at least $300?
Problem 19 Compare two models ★★★
The data points are (2, 14), (5, 23), and (8, 34). Model A is y = 3.4x + 7 and model B is y = 3x + 8. Find each model’s prediction at the three x-values and decide which model is closer overall.
Problem 20 Babysitting earnings ★★★
A trend line is drawn through (0, 10) and (8, 62). Write its equation, interpret the slope and intercept, and predict the earnings for 10 hours.
