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Error Intervals (Bounds)
The weight of a bag of potatoes is 15kg to nearest kg.
a)Write down the smallest possible weight of the bag of potatoes
Answer; 14.5kg (any smaller, e.g, 14.499999999998kg would be rounded DOWN to 14kg.
14.5kg is correctly rounded UP to 15kg
b)Write down the largest possible weight of the bag of potatoes
My answer; Greater than 14.5kg but less than 15.5kg; but a specific weight can't be given.
Their answer; 15.5kg
My question; How can it be 15.5kg? If it was 15.5kg it would have been rounded UP to 16kg (?).
Thanks. I thought that. But the answer given implied otherwise. I'll try to dig out the question and post it. One of those moments where you think, "darn! How can I do this when I'm forgetting basic algebra."
Thanks, Bob.
Thanks, Bob. And will do.
I suspect that rounding might come into this...
I've never heard of error intervals, but rounding is uppermost in my mind atm because I'm working on a tricky problem where rounding is critical in finding solutions.
Thanks. Ah, they are related to Bounds (upper bound/lower bound). Must be a UK thing. Rounding is the significant feature, but truncation is also a part of it.
I think you've arrived at the right answer.
What is 8.27685 doing in your list?
Bob
Thanks. Oh yeah, I forgot it began with 8.3! 8.999999.... shouldn't be there either!
Three buses, bus A, bus B and bus C all use the same bus stop.
A runs every 10 mins
B runs every 12 mins
C runs every 14 mins
All three are the bus stop at 11am
What time will all three buses next be at the bus stop
Q. What does ‘runs every 10 mins’ mean?
Thanks, Bob.
Here's the kind of thing we're doing;
https://www.mathsgenie.co.uk/resources/6-inequalities-regions.pdf
I'm on question 5 at the moment and finding it tricky
Sally used her calculator to work out the value of a number y
The answer on her calculator display began;
8.3
Complete the error interval for y
*
Does ‘began’ imply there is more to come after the 3?
Or could 8.3 be the answer on her calculator (could it begin AND END with 8.3?)
I’m thinking it implies it could be either, i.e, it might be 8.3, it might be more, so...
The answer on her calculator could be;
8.3
8.31
8.301
8.27685
8.999999999999999994
Etc, etc.
So...
The error interval is;
Equal to or greater than 8.3
Less than 8.4
?
Can the following fraction be simplified further?
Numerator; 2(x+3)
Denominator; 2(x+1)
Why does zero times anything equal zero?
I guess x times y means how many lots of y you have
2 times y means you have 2 lots of y
10 times y means you have 10 lots of y
Zero times y means you have zero lots of y
You have no lots of y
You have no y
I'm curious to have another look at the questions, but also;
We've been given a handout of expected topics in the next two papers, given what was in the first paper. It's from 1st Class Maths. But I don't know how reliable it is. And given the huge number of topics they've starred as very likely to unlikely (five stars down to one star) it looks like they're not just going on what topics have already come up. There was only around 20 questions on the first paper so there must be some other criteria for predicting what's likely to come up.
E.g. under 2 stars (pretty unlikely) there are around 40 topics listed.
Thanks, Bob.
Yeah, our teacher said somebody usually puts it online.
Does anybody else hate these?
Is it just me, or are they messy/awkward/UGLY/unsatisfying?
Is Paper 1, and the mark scheme, (May 24), available anywhere, now that the exam has taken place?
I've looked online but couldn't find it anywhere.
I came across the following inequality in this context;
x ≤ 6-2y
My instinct was to rearrange it to have y on the left hand side thus;
y ≤ -(1/2x) +3
Should I have bothered?
I guess I'm used to seeing it that way.
Thanks, Bob.
The question said;
"Simplify fully"
So which is simpler; (2x+3) /(x-3)?
or; 4x+6 / (x-3)?
I simplified an algebraic fraction to; 4x+6/(x-3)
But the answer given was 2(2x+3)/(x-3)
They hadn't expanded 2(2x+3) to 4x+6
Did I go too far, or did they not go far enough?
Thanks a lot, Bob.
Is the planet (Earth) dying?
Was it ever alive?
Before the first soil, before the first moss, or moss-like plant, or blue-green algae - basically before the first life forms that would attach themselves to the surface of the Earth, what was the surface like?
Was it smooth, like an enormous (almost) spherical stone? What was it’s composition, approximately?
And, back to the top, if every life form on Earth went extinct and all the corpses (including the plant ‘corpses’) decomposed, to dust (?) would the planet be just as it was 4-5 billion years ago before life arose on it?
"As x can anything you can equate the non x bits and separately the x bits"
x is a variable, yeah?
Are b and c not variables? Can they not be anything?
I know you've shown them to be 27,3, here, but how do I know when first looking at the problem that b and c are different from x (in terms of the latter being able to be anything)?
Is there no permuation of values where b and c could equal something different?
Surface Area
If the surface area of solid shape is 4cm^2 what can we infer about the shape?
Not a sphere (pi would lead to decimals)?
Same for cones and cylinders?
Pyramid?
Or does 4cm^2 have a square ‘ring’ to it? Should we be thinking cube/cuboid?
Also, at GCSE level (UK), or at any level for that matter, does 'solid shape' refer to 'straightforward' solid shapes, as opposed to the 3d versions of compound shapes?
Blue tit babies. Sounds great.
Thanks, Bob
Great answer. Thanks, Bob.
I think I'm getting there, understanding the first part. I'll need to come back for another look. And another