S1 Mock Paper - Q1

username120877

The weight of coffee in glass jars labelled 100g is normally distributed with mean 101.8g and standard deviation 0.72g. The weight of an empty glass jar is normally distributed with mean 260.0g and standard deviation 5.45g. the weight of a glass jar is independant of the weight of the coffee it contains.

Find the probability that a randomly selected jar weighs less than 266g and contains less than 100g of coffee. give your answer to 2 significant figures.

i have no answer to this so i dunno if im doing it right...

i worked out the weight less than 100 with (101.8,0.72^2)

then i worked out weight less than 266 with (260, 5.45^2)

after solving both i multiplying them together as they are independant and got 0.0054....is this correct?

Reply 1

Kelly^2

Sounds far too low.
What you need to do is standardise the values you have, then use the Z scores from the table of normal distribution. I haven't started the revision for this yet so can't go into any more detail as i don't have my books but it should be in your textbook.