X~N(8,25)

P( )=0.4

We need to find a.

I decided to use GC and standardize it to find a.

P( )=0.4

Since it is now standardized,

P( )

=1-2P( =0.4

P( =0.3

P( =0.7

So I used Ti84 InvNorm Function to get =0.5244

Which means is 10.622. However, the ans is 6.75.

Anyone can point out my mistake?

Thanks.