Estimate the product (1977 × 199) using the general rule.

The general rule says - round off each factor to its greatest place, then multiply the rounded-off factors.

So,

1977 is rounding off to the nearest thousands ⇒ 2,000 and 

199 is rounding off to the nearest hundreds ⇒ 200.

So, the estimated product of 1977 × 199 ≈ 2000 × 200 = 400000.