D1 January 2010 Q4

Notes

1M1 Pivot, p, chosen. List sorted, >p, p. <p or <p, p, >p. If only choosing 1 pivot per iteration M1 only

1A1 1^st pass correct and chosen next two pivots correctly for sublists >1

2A1ft 2^nd pass correct and chosen next two pivots correctly for sublists >1

3A1ft 3^rd pass correct and next pivot for sublist >1 chosen correctly.

4A1 cso.

Misread in part (a)

• If they have misread a number at the start of part (a), so genuinely miscopied and got for example 0.1 instead of 1.0 then mark the whole question as a misread – removing the last two A or B marks earned. This gives a maximum total of 9.
• If they misread their own numbers during the course of part (a) then count it as an error in part (a) but mark parts (b) and (c) as a misread. So they would lose marks in (a) for the error and then the last two A or B marks earned in (b) and (c) - giving a maximum of 8 or maybe 7 marks depending on how many marks they lose in (a).

The most popular misread is the one listed above – where 1.0 has changed to 0.1 giving
4.0  4.0  3.2  2.6  2.5  0.6  0.5  0.4  0.3  0.1   at the end of (a) for this one (b) and (c) are:

(b) Length 1: 4
Length 2: 4
Length 3: 3.2  0.6  0.1
Length 4: 2.6 0.5  0.4  0.3
Length 5: 2.5

(c) 18.2/4 = 4.55 so 5 bins, or total is 18.2 or 1.8 ‘spare’
Yes answer in (b) uses the minimum number of bins.

Alternate solutions for Question 4

Choosing middle left

Choosing first

OR (alternate choosing first)

Question 4 sorting into ASCENDING order (full marks if then reversed, otherwise MISREAD)

Middle left

Middle right

First (1)

First (2)

Notes

M1 left column & 1.0 in place

A1 0.6 & 0.5

A1 0.4

A1 All correct (c.s.o)