# Maths question about VARIANCE

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If a group of children have a mean score of 108 and the variance is 169. What range would you expect 95% of the children to score within?

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(Original post by

Do you know what variance is? Is there any more context for this question?

**Theloniouss**)Do you know what variance is? Is there any more context for this question?

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(Original post by

do you know what sort of distribution this is?

**arwaisfailing**)do you know what sort of distribution this is?

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(Original post by

okay great, so do you know where to use this info in ur graphical calculator?

**arwaisfailing**)okay great, so do you know where to use this info in ur graphical calculator?

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#8

(Original post by

If a group of children have a mean score of 108 and the variance is 169. What range would you expect 95% of the children to score within?

**anaindiemood**)If a group of children have a mean score of 108 and the variance is 169. What range would you expect 95% of the children to score within?

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#9

(Original post by

Unfortunately not😬

**anaindiemood**)Unfortunately not😬

then click F5 for DIST (distribution)

then click F1 for NORM (normal distribution)

then for this question, you need Ncd (normal cumulative distribution)

for all of this, if you have or don’t have any values in the table that shows, it makes no difference (so ignore & just follow what i’ve said above)

is this making sense? i want to help you guide urself to the answer rather than giving it to u straight so it’s helps a bit more, sorry if anything sounds patronising!!

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(Original post by

okay so using a graphical calculator, go into the STATS section

then click F5 for DIST (distribution)

then click F1 for NORM (normal distribution)

then for this question, you need Ncd (normal cumulative distribution)

for all of this, if you have or don’t have any values in the table that shows, it makes no difference (so ignore & just follow what i’ve said above)

is this making sense? i want to help you guide urself to the answer rather than giving it to u straight so it’s helps a bit more, sorry if anything sounds patronising!!

**arwaisfailing**)okay so using a graphical calculator, go into the STATS section

then click F5 for DIST (distribution)

then click F1 for NORM (normal distribution)

then for this question, you need Ncd (normal cumulative distribution)

for all of this, if you have or don’t have any values in the table that shows, it makes no difference (so ignore & just follow what i’ve said above)

is this making sense? i want to help you guide urself to the answer rather than giving it to u straight so it’s helps a bit more, sorry if anything sounds patronising!!

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#13

try plugging in ur values into that inverse normal section and tell me what u do, and i’ll lyk if your answer matches mine

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#14

(Original post by

To answer this question you probably have to assume that students' scores are normally distributed. You also have to guess whether the 95% of students means that 95% of students will score <= a particular score, or >= a particular score, or whether the 95% is supposed to be symmetrically arranged either side of the mean. I think the last of those options is most likely, in which case, the 5% of students not included in the central 95% will be divided equally between lower and upper tails of 2.5% each. What you then need to know is that, for a normal distribution, an upper tail of 2.5% starts 1.96 standard deviations above the mean, with similar reasoning for the lower tail. You will find these and similar % figures in a table of percentage points for the normal distribution, contained in textbooks and A level formula. booklets.

**old_engineer**)To answer this question you probably have to assume that students' scores are normally distributed. You also have to guess whether the 95% of students means that 95% of students will score <= a particular score, or >= a particular score, or whether the 95% is supposed to be symmetrically arranged either side of the mean. I think the last of those options is most likely, in which case, the 5% of students not included in the central 95% will be divided equally between lower and upper tails of 2.5% each. What you then need to know is that, for a normal distribution, an upper tail of 2.5% starts 1.96 standard deviations above the mean, with similar reasoning for the lower tail. You will find these and similar % figures in a table of percentage points for the normal distribution, contained in textbooks and A level formula. booklets.

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(Original post by

try plugging in ur values into that inverse normal section and tell me what u do, and i’ll lyk if your answer matches mine

**arwaisfailing**)try plugging in ur values into that inverse normal section and tell me what u do, and i’ll lyk if your answer matches mine

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#16

(Original post by

Hahhaa honestly the calculator confusion is making this a lot more complex than it needs to be I’m struggling🤣🤣

**anaindiemood**)Hahhaa honestly the calculator confusion is making this a lot more complex than it needs to be I’m struggling🤣🤣

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(Original post by

aw okay, tell me what you know and what ur unsure about

**arwaisfailing**)aw okay, tell me what you know and what ur unsure about

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#18

okay so,

data : variable (it’s always this)

tail: central (as the question does not say top 95% or bottom 95%, so you can assume it’s just the middle 95%)

area: 0.95 (says 95% in question)

standard deviation symbol: 13 (this is the square root of variance, so in this case, 13)

mean symbol: 108 (in question)

really hoping ur calculator looks similar to mine and this makes sense!

data : variable (it’s always this)

tail: central (as the question does not say top 95% or bottom 95%, so you can assume it’s just the middle 95%)

area: 0.95 (says 95% in question)

standard deviation symbol: 13 (this is the square root of variance, so in this case, 13)

mean symbol: 108 (in question)

really hoping ur calculator looks similar to mine and this makes sense!

Last edited by arwaisfailing; 1 month ago

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(Original post by

okay so,

data : variable (it’s always this)

tail: central (as the question does not say top 95% or bottom 95%, so you can assume it’s just the middle 95%)

area: 0.95 (says 95% in question)

standard deviation symbol: 13 (this is the square root of variance, so in this case, 13)

mean symbol: 108 (in question)

really hoping ur calculator looks similar to mine and this makes sense!

**arwaisfailing**)okay so,

data : variable (it’s always this)

tail: central (as the question does not say top 95% or bottom 95%, so you can assume it’s just the middle 95%)

area: 0.95 (says 95% in question)

standard deviation symbol: 13 (this is the square root of variance, so in this case, 13)

mean symbol: 108 (in question)

really hoping ur calculator looks similar to mine and this makes sense!

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**arwaisfailing**)

okay so,

data : variable (it’s always this)

tail: central (as the question does not say top 95% or bottom 95%, so you can assume it’s just the middle 95%)

area: 0.95 (says 95% in question)

standard deviation symbol: 13 (this is the square root of variance, so in this case, 13)

mean symbol: 108 (in question)

really hoping ur calculator looks similar to mine and this makes sense!

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