Question

Estimate $129\times 387$

Answer 1

Step 1: Rounding off $129$ and $387$ to the nearest hundred.

We know that to round off a number nearest to a hundred, we check the digit at the tens place.

If it is less than $5$, we consider the unit and tens digit to be, $0.$And if it is $5$ or more than $5$, we add $1$ to the digit at hundred places, and the ones and tens place becomes $0$.

So, in $129$, the digit at tens place is $2\text{i.e}$ less than $5$.

$\therefore$$129$ becomes $100$ after rounding off.

Similarly, in $387$, the digit at tens place is $8\text{i.e}$ more than $5$.

$\therefore$$387$ becomes $400$ after rounding off.

Step 2: Estimating $129\times 387$

The estimated value of $129$ is $100$ and $387$ is $400$

So, the estimated value of $129\times 387$$=100\times 400$

$=40000$

Hence, the estimated value of $129\times 387$ is $40000$