D1 question

I asked a similar question before but i cant seem to find that thread



For this question where did they get 2y>=2x + 9z from?

the total of all components is 6x + 9y + 12z

the components of type A is 2x + 4y + 3z

you want next to say 2x + 4y + 3z is greater than or equal to 40% of 6x + 9y + 12z

Yeah i got that:

2x + 4y + 3z >= 0.4 (6x + 9y + 12z)

But if you multiply by 5 you get:

10x + 20y + 15z >= 6x + 9y + 12z
11y >= -4x - 3z

?

0.4 is 2/5

ughghghfh yeah youre right i forgot about the 2. Thanks for reminding me

so its:

10x + 20y + 15z >= 12x + 18y + 24z
2y >= 2x - 9z

Do you have any ideas about the second question i posted?

ABDBCBA is a shorter route than ABDCA but it isn't the same length as the route in c,(ii).

(In fact the question seems very ill-posed - it's not possible for Xiong to both choose the shortest route and a route the same length as in c, (ii)).

ABDBCBA is a shorter route than ABDCA but it isn't the same length as the route in c,(ii).

(In fact the question seems very ill-posed - it's not possible for Xiong to both choose the shortest route and a route the same length as in c, (ii)).

the answer to c)ii) is 106km

ABDBCBA 20 + 15 + 15 + 18 + 18 + 38 = 124km

My answer still gets the same length, with an 'actual' route. So why is their's right and mine is wrong?

BA = 20, not 38, surely?
ABDCBA 20 + 15 + 33 + 18 + 20 = 106km

Because BD according to the original graph takes 35km, not 33. (I also now understand a bit more what they are getting at; will teach me to read the whole question next time and not just the bit I'm asked about!) You need to provide a route in terms of the original graph.

Yeah thats what i put: BA is 20, CBA = 38

BD = 15???

I have provided it in terms of the original though?

You wrote that:

ABDBCBA 20 + 15 + 15 + 18 + 18 + 38 = 124km

If you didn't mean that AB =20, BD = 15, DB = 15, ..., CB = 18, BA = 38, then I have no idea what that line of yours was supposed to mean.

My bad: I meant CD (this is why I hate trying to answer questions with attachments that you can't actually look at while answering the question!).

In terms of the original, ABDCBA has length 20 + 15 + 35 + 18 + 20 = 108. It only becomes 106 when you replace DC with DBC (reducing the journey from D to C from 35 to 33).

Ah that makes more sense - you mean DC = 35 but DBC = 33

Ok i think i see it now - they replaced DC with DBC on my route to get an 'actual' route. Right?
ABDCBA ----> ABDBCBA