[tex] a).\;1/24\;;\;1/40\;;\;1/15\;;\\
b).\;\underbrace{1/24+1/40+1/15}_{aduc\,la\,numitor\,comun\;\\
si\;amplific}=\frac{5+3+8}{120}=16/120=4/30=2/15[/tex]
c). 2/15 din lucrare . . . . . 1 ora
1/15 " " . . . . . 1/2 ora
15/15 " " . . . . . 15 * 1/2 = 7,5 ore