4.2 Estimating Sums &
Differences
What are some things that are often
rounded?
Target
We will use rounding to estimate sums and
differences.
Rounding Review!
5 or more, add one more!
4 or less, stay!
1,325
300
350
400
Vera went on a 3-day trip in which she
traveled 336 miles the first day, 423 miles
the second day, and 357 miles on the third
day. Is 300 or 400 a more reasonable
estimate for about how far she went on each
of the days?
Vera went on a 3-day trip in which she traveled 336
miles the first day, 423 miles the second day, and 357
miles on the third day.
Vera’s Distances
Miles Traveled
1st day
2nd day
3rd day
Rounded to
Nearest Hundred
When would you want to use an estimate instead of an
exact answer?
When you need to decide how many packages to buy
when items are sold in certain quantities.
The Empire State Building was completed in 1931.
From ground to tip it measures 1,250. At the top of the
building is a lightening rod which measures 204 feet.
Estimate the total height of the building.
Is the answer reasonable?
1. Write the numbers vertically (up and down).
2. Decide which place to round to. Round each
number.
3. Add or subtract the rounded numbers.
4. Check your answer for reasonableness.
The Washington Monument was completed in 1884.
About how many years after was the Empire State
Building completed?
10
How would rounding the dates to the nearest hundreds
change the usefulness of the estimate?
You Try!
Compare the years Illinois (1818) and
Wyoming (1890) acquired statehood.
You Try!
563
+ 375
You Try!
288
- 1 7 1
You Try!
645 + 253
You Try!
262 - 132
You Try!
952 - 402
You Try!
398 + 121
1. What are we studying today?
2. What did we learn?
3. What are the steps?
1. Write the numbers vertically (up and down).
2. Decide which place to round to. Round each
number.
3. Add or subtract the rounded numbers.
4. Check your answer for reasonableness.
Pg 94 - #9-12, 17, 18, 23, 24, 27, 29
CHALLENGE: Pg. 95 # 25