MRSM Trial 2025 Add Maths Paper 2, Question 11Linear Law

Solved on video in English · Form 4, Linear Law · 7:02 video

The question

(a)(i)

Table 1.1 shows the values of two variables x and y obtained from an experiment. The variables are related by y = px + r/(px), where p and r are constants. Table 1.1: x = 1, 2, 3, 4, 5, 6 ; y = 5.9, 4.2, 4.3, 4.6, 5.1, 5.9.

(a)(i) Based on Table 1.1, complete Table 1.2 (the xy row, given the x² row = 1, 4, 9, 16, 25, 36).

(a)(ii)

Table 1.1 gives x = 1, 2, 3, 4, 5, 6 and y = 5.9, 4.2, 4.3, 4.6, 5.1, 5.9 for y = px + r/(px).

(a)(ii) Plot xy against x², using a scale of 2 cm to 5 units on both axes. Hence, draw the line of best fit.

(b)(i)

Using the straight-line graph of xy against x² (from y = px + r/(px), where xy = p·x² + r/p):

(b)(i) Using the graph in (a)(ii), find p.

(b)(ii)

Using the straight-line graph of xy against x² (xy = p·x² + r/p, with p = 0.8429):

(b)(ii) Using the graph in (a)(ii), find r.

(c)

The variables are related by y = px + r/(px), with p = 0.8429 and r = 4.214.

(c) Hence, find the values of the gradient and y-intercept for another possible linear form for y = px + r/(px).

MRSM Trial 2025 Add Maths Paper 2, Question 11: the question as drawn in Eduly's video7:02

Part (a)(i)

Step 1

Compute xy = x·y for each column: x=1 → 5.9; x=2 → 8.4; x=3 → 12.9; x=4 → 18.4; x=5 → 25.5; x=6 → 35.4 (paired with x² = 1, 4, 9, 16, 25, 36).

Why this step

This row must be x × y because the straight line form we plot is xy against x². Watch for slips like x²·y or x + y.

Final answer

xy = 5.9, 8.4, 12.9, 18.4, 25.5, 35.4

Where students lose marks

Watch out: the row is x × y, not x²·y or x + y.

Part (a)(ii)

3 more steps, each with the reason for it, in the full solution

Final answer

Graph plotted (see video)

Where students lose marks

Watch out: plot xy against x², not x, use a uniform scale, and draw the line so the points balance on both sides.

Part (b)(i)

2 more steps, each with the reason for it, in the full solution

Final answer

p = 0.8429

Where students lose marks

Watch out: p is the gradient of the line, not the intercept.

Part (b)(ii)

2 more steps, each with the reason for it, in the full solution

Final answer

r = 4.214

Where students lose marks

Watch out: the y-intercept is r/p, not r. Multiply it by p to get r.

Part (c)

2 more steps, each with the reason for it, in the full solution

Final answer

gradient = 5, y-intercept = 0.8429

Where students lose marks

Watch out: for y/x against 1/x², the gradient is r/p and the intercept is p, the reverse of xy against x².

Watch every step of this question solved on video (7:02), with the reason behind each step and a box that checks your own answer.

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