Question

Give a rough estimate (by rounding off to nearest hundreds) and also a closer estimate (by rounding off to nearest tens) of $439+334+4317$.

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 $439$ to the nearest hundreds $=400$

Rounding off $334$ to the nearest hundreds $=300$

Rounding off $4,317$to the nearest hundreds$=4300$

On adding we get,

$400+300+4300=5000$.

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 $439$ to the nearest tens $=440$

Rounding off $334$ to the nearest tens $=330$

Rounding off $4,317$to the nearest tens$=4320$

On adding we get,

$440+330+4320=5090$.

Hence, using rounding off to hundreds answer is $5000$ and using rounding off to tens answer is $5090$.