Question

Estimate the total weight of two boxes that weigh 9.4 and 62.6 pounds using rounding and compatible numbers. which estimate is closer to the actual total weight? why?

Answer 1

With rounding:
$4$ is less than $5$ so we round it down to whole number:
$9.4\approx9$

$6$ is more than $5$ so we round it up to whole number:
$62.6\approx63$

Now we have to add rounded numbers
$63+9=72$

Without rounding:
$62.6+9.4$ to make it more visible I will write it differently:

$62+9+0.6+0.4$ is equal to $62.6+9.4$

we can see that $0.6+0.4$ is equal to $1$

so:
$62+9+1=72$

As you see in this example those equations are equal so it doesn't matter if you take rounded numbers or not, it may be different in case like $62.4+9.4$  ( $0.4$ is just an example it could be any other number between $0-4$ ) because in this case it will be equal $71$ and another example $62.5+9.5$ (in this case $0.5$ is just an example, it can be any other number between $5-9$ :) ) and here, answer for this equation is $73$.