While your composing that one I would like to post this one as well. I am confused on this one too
We want to find the z score in the table that corresponds to .20 [ or....at least as close as possible]
Looking at the table here : http://www.z-table.com/ .... we find that this corresponds to a z score of ≈ -.84
So....the 'formula" for our z score is
[ mass we are trying to find - mean ]
________________________________ = -.84 fill in what we know
std dev
[ mass we are trying to find - 55 ]
_______________________________ = -.84 multiply both sides by 4.2
4.2
mass we are trying to find - 55 = -3.528 add 55 to both sides
mass we are trying to find = 51.472 ≈ 51.5 g [ first answer ]
EDIT TO CORRECT A PREVIOUS ERROR !!!
Second one
[ age we are looking for - mean ]
____________________________ = z score
std dev
[age we are looking for - 32 ]
___________________________ = -1.2 multiply both sides by 6.2
6.2
age we are looking for - 32 = -7.44 add 32 to both sides
age we are looking for = 24.56 = 24.6 rounded to nearest tenth