Edexcel S3---9/06/05

Var [aX] = a² Var [X]

Just for the record I mean the following: -

Var [3X] = 9 Var [X]

BUT Var[X₁ + X₂ + X₃ ] = 3 Var [X]

...because they are separate observations of the variable as opposed to one observation getting scaled.

So say it said...time taken for a car to drive one mile is distributed X~ N(10,100)

What's the probability it takes less then 35 minutes for a car to drive the three mile journey from here to school. You are dealing with X₁ + X₂ + X₃ ~N(30,300) and not 3X ~ N(30,900).

Just for the record I mean the following: -

Var [3X] = 9 Var [X]

BUT Var[X₁ + X₂ + X₃ ] = 3 Var [X]

...because they are separate observations of the variable as opposed to one observation getting scaled.

So say it said...time taken for a car to drive one mile is distributed X~ N(10,100)

What's the probability it takes less then 35 minutes for a car to drive the three mile journey from here to school. You are dealing with X₁ + X₂ + X₃ ~N(30,300) and not 3X ~ N(30,900).

lol mine is
P1-100
P2-94
P3-91
P4-86
M1-95
S1-75 >> retaking
good luck im gona try n get down to some more past papers

yeh for example if a question says the weight of a women follow a normal (8,10). 3 women go into a lift. What is the distribution of there weight it would be

W~N(8+8+8,10+10+10)

but if it said a woman goes into the lift whose weight is three times that of a normal woman then

w~N(8+8+8, 9x10)

hajira do you have the mock s3 answers would be grateful if you could send it 2me