$2\mathrm{.}4$ on page $33($a$),($b$),($c$),($d$).$ For $($c$)$ and $($d$),$ use the formulas.

A$=($A$\backslash$cap B$)\backslash$cup $($A$\backslash$cap B$)$;

A

$=$

A

$\backslash$cap

B

$\backslash$cup

A

$\backslash$cap

B

$-$

;

P$($A$)=$P$($A$\backslash$cap B$)+$P$($A$\backslash$cap B$)$

P

A

$=$

P

A

$\backslash$cap

B

$+$

P

$($

A

$\backslash$cap

B

$-$

$)$

$.$

Among employees of a certain firm, $70\%$ know C$/$C$++,60\%$ know Fortran, and $50\%$ know both languages. What portion of programmers

$($a$)$ does not know Fortran?

$($b$)$ does not know Fortran and does not know C$/$C$++?$

$($c$)$ knows C$/$C$++$ but not Fortran?

$($d$)$ knows Fortran but not C$/$C$++?$