To multiply numbers in scientific notation, first multiply the numbers that do not have a base of 10 and then add the exponents of the bases of 10. Essentially:
![(a \cdot 10^b)(c \cdot 10^d)](https://img.qammunity.org/2019/formulas/mathematics/middle-school/dhillxajmltfs71ag62n0fm426m0bpsyot.png)
![(a \cdot c) \cdot (10^((b + d)))](https://img.qammunity.org/2019/formulas/mathematics/middle-school/yzdimw6ccx5udjplvnnw44eenewnofavqq.png)
In this case, we see that the numbers that do not have bases of 10 are 2.3 and 3.1. Multiplying these numbers gives us:
![2.3 \cdot 3.1 = 7.13](https://img.qammunity.org/2019/formulas/mathematics/middle-school/o9jpydjif6r4phuz00430gckvmxr5xsgs5.png)
The exponents on the bases of 10 are -5 and 1. Adding these exponents gives us -4, which we can add to our final base of 10.
Thus, our answer is:
![\boxed{7.13 \cdot 10^(-4)}](https://img.qammunity.org/2019/formulas/mathematics/middle-school/krc2l2bth73la8vee4dy2062t8wsb1kfex.png)