Writing Linear Equations and Scatter Plots: math test solutions, Grade 9 – download the PDF

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Test solutions with the detailed point scale. Add up your points and spot what to review.

Suggested time: 45 minutes. Out of 20 points. Calculator allowed only when the problem says so.

Sommaire

(a) $y - 3 = -4(x - 2)$ (0.5 pt), so $y = -4x + 11$ (1 pt).

(b) $y + 5 = 2(x + 1)$ (0.5 pt), so $y = 2x - 3$ (1 pt).

(a) $m = \dfrac{-1 - 7}{3 - (-1)} = -2$ (1 pt). $y - 7 = -2(x + 1)$, so $y = -2x + 5$ (1 pt).

(b) $-2x + 5 = 0$, so $x = 2.5$ (1 pt).

(a) The points rise: strong positive correlation (1 pt).

(b) Predicted $2.2(3) + 1 = 7.6$; residual $8 - 7.6 = 0.4$ (1 pt).

(d) $2.2(10) + 1 = 23$ cm (0.5 pt). Day 10 is outside the data (extrapolation), so growth may not stay linear (0.5 pt).

(a) No, correlation does not prove causation (1 pt).

(b) Hot weather, which brings more swimmers and more cone sales (1 pt).

(a) $2 \le 3$, so $D(2) = 5$ (0.5 pt).

(b) $5 + 1.5(4) = 11$, so $11 (1 pt).

(d) $1.5x + 0.5 = 14$, so $x = 9$ miles (1.5 pt).

Vertex: $(-2, -4)$ (1 pt). y-intercept: $|2| - 4 = -2$ (1 pt). x-intercepts: $|x + 2| = 4$, so $x = 2$ or $x = -6$ (1 pt).

Test yourself: quick challenge for Grade 9