Mia 15
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Q5) Decode the message received by Space Defence Control.
MKW PWCCFQ USFGWJOWWM
LU FSSARFGKLQC SOWFUW
UWQH KWOS XW
QWWH PRAW CFOFGMLG
ABQFDRBMU XLMK KLCK
USWWH OFUWA CBQU

Q6) In a multiple choice test of 25 questions, four marks are given for each correct answer and two marks deducted for each wrong answer.
One mark is deducted for any question which is not attempted.

James scores 55 marks and wants to know how many questions he got right. He can't remember how many questions he did not attempt, but he doesn't think it was very many.
How many questions did James get right?

my working out:
total questions = 25
correct = 4
incorrect = -2
not attempted = -1

questions attempted = q
correct = c
incorrect = q-c
not attempted = 25-q

55= 4c - 2(q-c) - 1(25-q)
55= 4c - 2q+2c -25 + q
55 = 6c -q -25
80 = 6c -q

and Idk what to do next cause I have the answer but idk how to get there
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Sonika000
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he got 13 questions correct as he would have definitely got 4 marks for each correct answer. So divide 55/4=13.75 cant have any 0.75 mark so must be 13
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mqb2766
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(Original post by Mia 15)
Q5) Decode the message received by Space Defence Control.
MKW PWCCFQ USFGWJOWWM
LU FSSARFGKLQC SOWFUW
UWQH KWOS XW
QWWH PRAW CFOFGMLG
ABQFDRBMU XLMK KLCK
USWWH OFUWA CBQU

Q6) In a multiple choice test of 25 questions, four marks are given for each correct answer and two marks deducted for each wrong answer.
One mark is deducted for any question which is not attempted.

James scores 55 marks and wants to know how many questions he got right. He can't remember how many questions he did not attempt, but he doesn't think it was very many.
How many questions did James get right?

my working out:
total questions = 25
correct = 4
incorrect = -2
not attempted = -1

questions attempted = q
correct = c
incorrect = q-c
not attempted = 25-q

55= 4c - 2(q-c) - 1(25-q)
55= 4c - 2q+2c -25 + q
55 = 6c -q -25
80 = 6c -q

and Idk what to do next cause I have the answer but idk how to get there
You have 1 equation in two unknowns, which means there are multiple solutions. But the solutions are integers.
Can you think how
80+q = 6c
You must have 25>=q>=c. 80+q must be divisible by 6.

For the code one, I'm assuming monoalphabetic? The first word is fairly straightforward, and a bit of word spotting / letter frequency analysis gets you the rest.
Last edited by mqb2766; 4 weeks ago
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Sonika000
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actually mayb not dont know lol re read the question dont think my answer is right
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DFranklin
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(Original post by mqb2766)
You have 1 equation in two unknowns, which means there are multiple solutions. But the solutions are integers.
Can you think how
80+q = 6c
You must have 25>=q>=c. 80+q must be divisible by 6.

For the code one, I'm assuming monoalphabetic? The first word is fairly straightforward, and a bit of word spotting / letter frequency analysis gets you the rest.
I thought the code was quite hard (I cheated and used a tool). The frequencies are quite a way from the ordering I know of for the English language, and

Spoiler:
Show
The fact that the second word seems to be made up

is also pretty mean here.
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DFranklin
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(Original post by Mia 15)
Q6) In a multiple choice test of 25 questions, four marks are given for each correct answer and two marks deducted for each wrong answer.
One mark is deducted for any question which is not attempted.

James scores 55 marks and wants to know how many questions he got right. He can't remember how many questions he did not attempt, but he doesn't think it was very many.
How many questions did James get right?
Here's how I'd solve this:

What does James score if he gets every question right? From there, how much does his score go down if you change a right answer to a wrong answer?
Use this to calculate how many questions he'd need to get wrong to score below 55.
Now, how much does his score go up by if you change a *wrong* answer to a "no answer"?
So how many of those wrong questions would you need to change to "no answer" to get an answer of exactly 55?
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mqb2766
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(Original post by DFranklin)
I thought the code was quite hard (I cheated and used a tool). The frequencies are quite a way from the ordering I know of for the English language, and

Spoiler:
Show
The fact that the second word seems to be made up

is also pretty mean here.
Sure, word / vowel spotting (guided by frequencies) is the obvious way for small texts.
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