Penny has 3 red 5 green & 7 black pencils in her case. She takes 1 pencil out
at random & puts the pencil back into the case she does this 30 times. how many
pencils would she expect to be 1. green 2. red . 3 black
She has 3+5+7 = 15 pencils, so
or 
of the pencils are
red, so of the time she will pick a red pencil.
of 30 times is 6 times. So she would expect to
get a red pencil about 6 of the 30 times.
or 
of the pencils are
green, so of the time she will pick a green pencil.
of 30 times is 10 times. So she would expect to
get a green pencil about 10 of the 30 times.
of the pencils are black, so of the time she will pick a black pencil.
of 30 times is 14 times. So she would expect to
get a black pencil about 14 of the 30 times.
[ Of course she won't get exactly that with every 30 times she gets a pencil,
but it she took out a pencil 30 times every day for a year, and kept a record
of how many of each color she drew out every day, the average would be very
close to an average of 6 reds per day, 10 greens, per day, and 14 blacks per
day. Not exactly, but close.]
Edwin
