## Chemistry: A Molecular Approach (3rd Edition)

$1.59 \times 10^{-2}$
1. Rearrange the numbers to have the same exponent part, and then we simply make a common addition and subtraction $1.87 \times 10^{-2} + 2 \times 10^{-4} -3 \times 10^{-3} =1.87 \times 10^{-2} + 0.02 \times 10^{-2} -0.3 \times 10^{-2} = 1.59 \times 10^{-2}$