Edexcel D1 - 17th June, 2016 [Exam discussion]

Original post by target21859

Someone asked this before but it wasn't answered. Is there an equation for the maximum number of passes for a bubble sort?

You mean maximum number of swaps? There isn't a maximum number of passes.

max. swaps is

\frac{n(n-1)}{2}

Reply 222

Original post by NotNotBatman

You mean maximum number of swaps? There isn't a maximum number of passes.

max. swaps is

\frac{n(n-1)}{2}

Why did you use the summation of 'r' for that?

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Reply 223

Original post by NotNotBatman

You mean maximum number of swaps? There isn't a maximum number of passes.

max. swaps is

\frac{n(n-1)}{2}

For question 7(e) why did they move activity J? I thought because it was a critical activity that had a start time of 15 and end time of 22, it had to always be between those values as it has no float. So, how come in the marks scheme they allowed it to start at 17 and end at 24? Thanks in advance!

June 2014 (IAL)

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Reply 224

Original post by Glavien

Why did you use the summation of 'r' for that?

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If you want to sort numbers in descending order, the maximum number of swaps comes from a list that is in ascending order. e.g sorting the numbers 2,1,3,4 and 5 in descending order; for the maximum number of swaps the initial list has to be 1,2,3,4,5.
In the first pass there will be 4 comparisons then 3 then 2,1. So 1+2+3+4, sum of the first natural numbers, where the first term is (n-1)

If you accept that

\sum_{r=1}^{n}r = \frac{n}{2}(n+1)

but there aren't dealing with numbers up to

n

, but

n-1

, so replace any

n

in the formula with

(n-1)

So

\sum_{1}^{n}(n-1) = \frac{n-1}{2}[(n-1)+1] = n\frac{n-1}{2}

EDIT: If the LaTEX is illegible, try pressing quote to see if that works.

(edited 7 years ago)

Reply 225

Original post by Glavien

For question 7(e) why did they move activity J? I thought because it was a critical activity that had a start time of 15 and end time of 22, it had to always be between those values as it has no float. So, how come in the marks scheme they allowed it to start at 17 and end at 24? Thanks in advance!

June 2014 (IAL)

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The critical time is 22, but the question says within 25 days, so you can delay the project by 3 days.

Reply 226

Original post by NotNotBatman

The critical time is 22, but the question says within 25 days, so you can delay the project by 3 days.

Ohh, so every activity has an extra float of 3?

Reply 227

Original post by Glavien

Ohh, so every activity has an extra float of 3?

No, but the total extra float for all activities combined is 3.

Reply 228

Original post by NotNotBatman

No, but the total extra float for all activities combined is 3.

Ohh, thanks for that! :smile:

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Reply 229

Just found a very juicy linear programming question I thought worth sharing

https://gyazo.com/dd50f9bef7cc5f770da7f0a05488d71b

Reply 230

Quickest chapter to learn? From a string pure background. Need 15 ums ish.

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Reply 231

Original post by physicsmaths

Quickest chapter to learn? From a string pure background. Need 15 ums ish.

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Dijkstras algorithm/route inspection

Reply 232

Original post by iMacJack

Dijkstras algorithm/route inspection

Cheers mate appreciate.
How many marks could I rack up learning this?

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Reply 233

Original post by physicsmaths

Cheers mate appreciate.
How many marks could I rack up learning this?

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Dependent on the paper probably around 20 marks? It all depends on how the marks are allocated but i'd say a secure 15 marks, how comes you only need 15 ums?

Reply 234

Original post by iMacJack

Dependent on the paper probably around 20 marks? It all depends on how the marks are allocated but i'd say a secure 15 marks, how comes you only need 15 ums?

Mainly duento getting 95-100 On C1-4 FP1-3 M1-3 so I am doing AFM this year and I am confident in getting 95 ish M4-5 and thing I have gotten a B in S3 so I need to just get enough for the 480 overall for 3A*s aggregate in Maths FM and AFM which is 10 UMS in D1/2 and around a decent amount of UMS in S4. Stats and decision ain't really my thing.

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Reply 235

Original post by physicsmaths

Mainly duento getting 95-100 On C1-4 FP1-3 M1-3 so I am doing AFM this year and I am confident in getting 95 ish M4-5 and thing I have gotten a B in S3 so I need to just get enough for the 480 overall for 3A*s aggregate in Maths FM and AFM which is 10 UMS in D1/2 and around a decent amount of UMS in S4. Stats and decision ain't really my thing.

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Impressive, well done :biggrin:

Reply 236

Original post by iMacJack

Impressive, well done :biggrin:

Cheers, good luck for this exam btw, seems like a very tedious exam!

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Reply 237