Question

Give a rough estimate (by rounding off to nearest hundreds) and also a closer estimate (by rounding off to nearest tens): $4,89,348-48,365$

Answer 1

Step $1$ : Rounding off to hundreds.

If the tens digits are $0,1,2,3$ or $4$ then round down to the previous hundred, and if the tens digits are $5,6,7,8$ or $9$ then round up to the next hundred.

Rounding off $4,89,348$ to the nearest hundreds$=4,89,300$

Rounding off $48,365$ to the nearest hundreds $=48,400$

On subtracting,

$4,89,300-48,400=4,40,900$

Step $2$ : Rounding off to tens.

If the one's digits are $0,1,2,3$ or $4$ then round down to the previous ten, and if the one's digits are $5,6,7,8$ or $9$ then round up to the next ten.

Rounding off $4,89,348$ to the nearest tens $=4,89,350$

Rounding off $48,365$ to the nearest tens $=48,370$

On subtracting,

$4,89,350-48,370=4,40,980$

Hence, using rounding off to hundreds answer is $4,40,900$ and using rounding off to tens answer is $4,40,980$.