Chris Graham

Chris Graham commented on Find the equation of a line through two points - negative gradient 8 years, 4 months ago

I've changed some of the simplification rules in the advice, corrected the calculation for the gradient and other inconsistencies with regards to the order of points A and B. Fixed some typos.

Chris Graham commented on Find the equation of a line through two points - positive gradient 8 years, 4 months ago

The points A and B should be switched; it doesn't make sense to describe the leftmost point as B, and in fact the gradient is calculated from A to B in the advice. There are places in the advice where $y_1-y_2$ needs to be inverted.

Chris Graham on Find the equation of a line through two points - positive gradient 8 years, 4 months ago

Gave some feedback: Has some problems

Chris Graham on Use speed and distance to calculate time 8 years, 4 months ago

Gave some feedback: Has some problems

Chris Graham commented on Use speed and distance to calculate time 8 years, 4 months ago

Context is good, and the variables are realistic.

"We can rearrange the formula for average speed to give us the formula for the time taken" - again I would give the speed/distance/time pyramid here, and then pick out the relevant equation.

Chris Graham on Calculate density given mass and volume 8 years, 4 months ago

Gave some feedback: Has some problems

Chris Graham commented on Calculate density given mass and volume 8 years, 4 months ago

At this level, I think it would be appropriate to add the classic mass/density/volume pyramid as an image in the step and all 3 equations, then let the student pick out the equation that they need to use. 

The advice is a little wordy: it takes the first 3 paragraphs and equation to explain that 1kg is 1000g. 

The question desperately needs a bit of context to make it interesting. There are many, many possibiities. See e.g. these Geoscience examples: https://serc.carleton.edu/mathyouneed/density/densitysp.html

Chris Graham on Geometric Sequence - negative ratio 8 years, 4 months ago

Gave some feedback: Has some problems

Chris Graham commented on Geometric Sequence - negative ratio 8 years, 4 months ago

Lots of problems with this:

In the question,

• The answer for (b) appears to use the wrong value for a.
• The prompt in (c) asks a term, but then has "common ratio = ..." before the gap.

In the advice,

• I would prefer the table cells to contain the calculation for the common ratio, rather than below, and express as a fraction, e.g. $\frac{-12}{36}=-3$.
• The values for $a_n$ appear to be wrong in the table.
• "Common ratio as..." then seems to give the wrong common ratio (wrong sign at least).

Chris Graham on Square and cube numbers 8 years, 4 months ago

Gave some feedback: Ready to use