Christian Lawson-Perfect

Christian Lawson-Perfect on Estimate the mean and find the modal class for grouped data 8 years, 5 months ago

Gave some feedback: Ready to use

Christian Lawson-Perfect on Estimate the mean and find the modal class for grouped data 8 years, 5 months ago

Saved a checkpoint:

I've changed the wording a bit to make it clearer.

I've changed "stage 1 average" to "stage 1 grade", because it could be confusing.

Christian Lawson-Perfect on Lowest common multiples: train timetable example 8 years, 5 months ago

Gave some feedback: Has some problems

Christian Lawson-Perfect on Lowest common multiples: train timetable example 8 years, 5 months ago

Saved a checkpoint:

Part a is a bit too simple for an incoming university student. 

This question should focus just on calculating least common multiples. Remove part a, leaving the nice wordy question. You could have another very simple separate question asking to find the LCM of two numbers when:

• they're coprime;
• their GCD is bigger than 1 but not equal to either number;
• one is a multiple of the other.

I think it should be "platform A" instead of "track A".

I got periods of 12 and 6 minutes for the two platforms - could you make sure that the LCM isn't either of the given numbers?

Christian Lawson-Perfect on Calculate a student discount 8 years, 5 months ago

Gave some feedback: Has some problems

Christian Lawson-Perfect on Calculate a student discount 8 years, 5 months ago

Saved a checkpoint:

I don't think anyone in the history of shopping has had a voucher for a 12% discount. Pick multiples of 5%.

The line in the advice about not rounding until the end is incorrect - in this instance you can round off the discount before subtracting it from the original price. If you were subtracting two discounts, or performing a further calculation with the discounted price, you might encounter problems. 

"This does not make sense in the real world" needs to be more precise - something like "The shop would round this discount to the nearest penny" would do.

I don't think I agree with "Method 1 is a bit simpler and more appropriate to use." - simplicity is in the eye of the beholder! Just briefly describe each method instead: "the first method involves working out the discounted price as a percentage of the original, while the second method calculates the value of the discount and subtracts that from the listed price."

Christian Lawson-Perfect on Use the quadratic formula to solve an equation in terms of an unknown variable 8 years, 5 months ago

Gave some feedback: Has some problems

Christian Lawson-Perfect on Use the quadratic formula to solve an equation in terms of an unknown variable 8 years, 5 months ago

Saved a checkpoint:

The marking is set up wrong: $k(-6)$ is the application of the function $k$, not $-6 \times k$. You can avoid this by writing $(\ldots)k$ instead of $k(\ldots)$.

It's not obvious what order you should enter the roots. The best I can come up with for a hint is "Assuming $k$ is positive, enter the lowest root first." I can't think how to be any clearer without giving a hint about the form of the answer.

You need \left and \right around brackets to make sure they stretch to fit around fractions.

Put the quadratic formula in the advice just before you list the values for $a$, $b$ and $c$.

Christian Lawson-Perfect on Calculate the measures of central tendency for a sample 8 years, 5 months ago

Gave some feedback: Ready to use

Christian Lawson-Perfect on Calculate the measures of central tendency for a sample 8 years, 5 months ago

Saved a checkpoint:

A good simple question.

Here's a simpler way of making sure you've got a unique mode: generate a random set of 19 values. Find a modal value of that set (there might be more than one), and add another instance of that value to get a list of 20 items with a unique mode.