I have two probability questions I have had a go at, Can someone have a look and see if they are correct or where i'm gonig wrong.

Mean length 10cm s.d 4mm - Bar 1

Mean length 20cm sd 6mm - Bar 2

So probability of picking bar 1 & bar 2 at randomand the total length being greater than 30.8cm

so add mean[FONT=MathJax_Math-italic] =[/FONT] 30cm

s.d =1cm

(30.8-30)/1

=0.8

using z table = 0.2119

Also difference in length of two random bars from the same as above being less than 9.8,

so Minus then

mean=10cm

s.d = 0.2cm

(9.8-10)/0.2

=-1

using -z table i get = 0.1587

sorry not used correct symbols on phone and doesn't seem to want to work.

Can somebody check these are correct.

thanks

Andy