Grade 8 · Statistics & probability

Scatterplots and trend lines practice

Scatterplots and trend lines is a grade 8 math skill aligned to Common Core standard 8.SP.A.3: use the equation of a linear model to solve problems in the context of bivariate measurement data, interpreting the slope and intercept. Below are 8 practice questions with answers and step-by-step explanations, drawn from the 18 scatterplots and trend lines problems our math games drill.

CCSS 8.SP.A.318 questions in the bank
Sample questions

Try 8 for free

Question 1easy

A line of best fit for the number of lawns Jaden mows xx and his savings yy in dollars is y=15x+40y = 15x + 40. According to the line, how many dollars did Jaden have saved before mowing any lawns?

At x=0x = 0 lawns, y=40y = 40: the yy-intercept is the starting savings.

Question 2easy

A trend line for hours studied xx and quiz score yy is y=4x+62y = 4x + 62. What score does the line predict for a student who studies 33 hours?

Substitute x=3x = 3: y=4(3)+62=12+62=74y = 4(3) + 62 = 12 + 62 = 74.

Question 3easy

A trend line predicts that a bakery will sell 7575 bagels on Monday. The bakery actually sells 7979 bagels. What is the residual (actual value minus predicted value)?

Residual == actual - predicted =7975=4= 79 - 75 = 4.

Question 4easy

A line of best fit relating hours of practice xx to free throws made yy is y=6x+10y = 6x + 10. According to the line, each additional hour of practice adds about how many free throws?

The slope of y=6x+10y = 6x + 10 is 66: the predicted change in free throws for each extra hour of practice.

Question 5easy

A trend line for the daily high temperature xx in degrees and cups of lemonade sold yy is y=2x60y = 2x - 60. For a predicted 100100 cups sold, what should the temperature be?

Solve 100=2x60100 = 2x - 60: 2x=1602x = 160, so x=80x = 80 degrees.

Question 6easy

A trend line for the number of car washes a club holds xx and the club's funds yy in dollars is y=75x+120y = 75x + 120. According to the line, how many dollars did the club have before holding any car washes?

At x=0x = 0, y=120y = 120 dollars: the yy-intercept is the starting amount.

Question 7easy

A trend line for miles jogged xx and calories burned yy is y=90x+20y = 90x + 20. How many calories does the line predict for a 44-mile jog?

y=90(4)+20=360+20=380y = 90(4) + 20 = 360 + 20 = 380 calories.

Question 8easy

A trend line predicts Mia will spell 1818 words correctly in a spelling bee. She actually spells 2121 words correctly. What is the residual (actual minus predicted)?

Residual =2118=3= 21 - 18 = 3 words.

Play it

Math games for Grade 8

Questions like these are served inside our head-to-head math games.

Drill it inside a game.

The free placement test finds your level, then every match serves scatterplots and trend lines questions at exactly the right difficulty.