Estimate the product $758\times 6784$ using the general rule.

Given product is $758\times 6784$.

For rounding off to nearest hundreds,we first check the digit at ten's place.If the digit at ten's place is less than $5$ then we replace its ten's and one's place by zero but if the digit at ten's place is $\ge 5$ then we add $1$to hundred's place digit and then replace ten's place and one's place by zero.

For rounding off to nearest thousands,we first check the digit at hundred's place.If the digit at hundred's place is less than $5$ then we replace its hundred's, ten's and one's place by zero but if the digit at hundred's place is $\ge 5$ then we add $1$to thousand's place digit and then replace hundred's, ten's place and one's place by zero

Using general rule,

$\begin{array}{rcl}758& \to & 800\\ 6784& \to & 7000\\ So,758\times 6784& =& 800\times 7000\\ & =& 5600000\end{array}$

Hence, using the general rule :$758\times 6784=5600000$.