Answer:
31.
[tex]6.139\times 10^-^7\\\\or\: 613.9\times 10^-^9[/tex]
29.
[tex]1.806 \times 10^2^5[/tex]
Step-by-step explanation:
31.
[tex]6.83\times\:10^{-7}-6.91\times\:10^{-8}\\\\10^{-7}=\frac{1}{10^7}\\\\=6.83\times\frac{1}{10^7}-10^{-8}\times\:6.91\\\\10^{-8}=\frac{1}{10^8}\\\\=6.83\times\frac{1}{10^7}-6.91\times\frac{1}{10^8}\\\\6.83\times\frac{1}{10^7}=0.000000683\\\\6.91\times \frac{1}{10^8}=0.0000000691\\\\=0.000000683-0.0000000691\\\\=0.0000006139\\\\= 6.139\times 10^-^7[/tex]
29.
[tex](2.1\times 10^1^6)\times(8.6\times 10^8)\\\\10^{16}\times \:10^8=\:10^{16+8}\\\\=2.1\times \:8.6\times \:10^{16+8}\\\\\mathrm{Add\:the\:numbers:}\:16+8=24\\=2.1\times \:8.6\times \:10^{24}\\\\\mathrm{Multiply\:the\:numbers:}\:2.1\times \:8.6=18.06\\=10^{24}\times \:18.06\\\\10^{24}=1.0E24\\\\=18.06\times \:1.0E24\\\\=1.806E25[/tex]
