Video Transcript
Ethan has to deliver mail to 415
houses. He delivered it to 82 houses on one
street and 107 houses on another. Pick the best estimate for the
number of houses he still has to deliver mail to: 100, 400, 200, 300, 600. After that find the exact number of
houses left: 522, 163, 333, 226, or 604.
Let’s start with the estimate. Ethan has to deliver mail to 415
houses. Let’s round this to the nearest
100. If we sketch a number line of 400
to 500, where would 415 fall on this number line. 415 would fall closer to 400 than
500. To round 415 to its nearest 100, we
would round it to 400.
We also know that he’s already
delivered 82 houses on one street. Let’s round 82 to the nearest
100. Where does 82 fall between zero and
100? 82 is closest to 100. We would round 82 to 100. And on another street, Ethan has
already delivered 107 houses their mail. On a number line, where does 107
fall between 100 and 200? 107 falls much closer to 100 than
200. So we would round 107 to 100.
Now that we’ve done all this
rounding, it’s time to put the information together. Here, we could say that Ethan has
to deliver mail to about 400 houses and he’s already delivered mail to how many
houses. These two numbers — both of our
100s — represent the number of completed houses. He’s already completed about 200
houses from his wrap.
To find out how many he has
remaining, we would subtract the completed from how many he had to start with: 200
from 400. 400 minus 200 equals 200. The best estimate for the number of
houses he still has to deliver mail to is 200.
For the second half of this
question, we need to find the exact number of houses remaining. We take the 415 and subtract
82. Five minus two equals three. One minus eight is not
possible. So we borrow from our hundreds
place turning that four into a three. And then, we would say 11 minus
eight which equals three. And finally, in our hundreds place,
three minus zero equals three.
All of a sudden, you notice that
333 is one of our answer choices. But it’s not the answer because
we’re not finished. We’ve only subtracted the first
street that Ethan delivered mail to. We need to take this 333 and
substract the 107 houses he delivered mail to from the other street.
Starting in the ones place, three
minus seven is not possible. We’ll borrow from our tens
place. Instead of three tens, we will have
two tens and 13 ones. 13 minus seven equals six. In the tens place, we now have two
minus zero, which equals two. And in our hundreds place, three
minus one equals two.
The exact number of houses Ethan
has remaining is 226.
