Write y = mx + b from a table, graph or story, and say what m and b mean

Answer Key - Grade 8 Math Worksheet - Challenge Me

Circle the best answer, or write your answer on the line.

1. Read this first

   Use the table

   input: x	output: y
   5	13
   1	5
   8	19

2. 1.

   Bo's math-club table shows a line, with uneven steps and no row for x = 0. What rule, written as y = mx + b, gives every row?

   y = 2x + 3
3. 2.

   Esme's math-club table shows a line, with uneven steps and no row for x = 0. What rule, written as y = mx + b, gives every row?

   y = 0.75x + 3
4. 3.

   Luz draws a line on a grid with negative numbers. Points A and B are marked, but neither is on the y-axis. What rule, written as y = mx + b, gives this line?

   y = 2x − 9
5. 4.

   Water freezes at 32 °F (0 °C) and boils at 212 °F (100 °C). Milo wants a rule for any temperature. What rule gives F from C, as F = mC + b?

   F = 1.8C + 32
6. 5.

   On a steady ride, Pia is 4 km from home at minute 10, 13 km at minute 40. Let x be minutes, y km. What rule gives y, as y = mx + b?

   y = 3x ÷ 10 + 1
7. 6.

   Ren uses F = 1.8C + 32 to change °C into °F. What does the 1.8 tell you?

   • Each 1 °C warmer is 1.8 °F warmer
   • Water freezes at 1.8 °F
   • 1.8 °C is the same as 32 °F
8. 7.

   On a ride, Zee's distance from home follows y = 0.4x + 2, in km after x minutes. What does the 2 tell you?

   • The ride takes 2 minutes
   • Zee was already 2 km from home at minute 0
   • Zee rides 2 km each minute
9. 8.

   Bo makes up a story for y = 5x + 20, with x in days. Which story fits the rule?

   • A jar starts with 20 beads, and 5 beads are added each day
   • A jar holds 25 beads, and none are added
   • A jar starts with 5 beads, and 20 beads are added each day
   • A jar starts empty, and 5 beads are added each day
10. 9.

    Esme makes up a story for y = -50x + 600, with x in hours. Which story fits the rule?

    • A bottle holds 50 mL, and 600 mL is drunk each hour
    • A bottle holds 600 mL, and 50 mL is added each hour
    • A bottle holds 650 mL in all
    • A bottle holds 600 mL, and 50 mL is drunk each hour
11. 10.

    Jun makes up a story for y = 1.5x + 4, with x in weeks. Which story fits the rule?

    • A seed starts at 0 cm and grows 1.5 cm each week
    • A plant is 5.5 cm tall and stops growing
    • A plant is 4 cm tall and grows 1.5 cm each week
    • A plant is 1.5 cm tall and grows 4 cm each week