a positive multiplied by a negative is a negative: 2.5+(-7.9)=2.5-7.9
and negative times a negative is a poisitive: 3.7-(-12.4)=3.7+12.4
for fractions if you have mixed numbers you multiply that big number by the denomintator and add it with the numberator: [tex]20 \frac{5}{16} [/tex] =[(20x16)+5]/16
