[tex]827 \times 4 \approx820 \times 4[/tex]
[tex]820 \times 4 = 800 \times 4 + 20 \times 4 \\ 820 \times 4 = 3200 + 80 \\ 820 \times 4 = 3280[/tex]
[tex]827 \times 4 \approx3280[/tex]
In reality it's just that additional 4 sevens,so
[tex]827 \times 4 = 820 \times 4 + 4 \times 7 \\ 827 \times 4 = 3280 + 28 \\ 827 \times 4 = 3308[/tex]
