Adding
Decimals
Decimals
Add 3.4 + 2.6
6
5.0−2.75
2.3
Estimate the sum of 4.3 + 3.8 by rounding to the nearest whole number.
8
What is the "commutative property of addition"?
"Order of addends can be changed without changing sum"
Mia bought pencils costing $1.25 and a notebook for $2.40. How much did she spend?
$3.65
Add 12.75+0.25
13
10.25−0.75
9.50
Use compatible numbers to estimate 19.7+30.3
compatible numbers give 20+30=50
What does the "associative property of addition" mean?
"Grouping of addends doesn't change sum, "
A jogger runs 2.52 miles on Monday and 3.75 miles on Tuesday. How many miles total?
6.25 miles
Add 6.83 + 2.19
9.02
8.62−3.495
3.125
Estimate the difference of 23.49−7.88 by rounding tenths decimal place
23.5−7.9≈15.6
Define "compatible numbers"
numbers that are easy to work with in yo head
A tank held 50.0 liters. After use it held 18.375 liters. How many liters were used?
31.625 liters used;
Add
45.607 + 3.298
48.905
100.003−12.457
87.546
Which is a better estimate for 6.78+4.96 — rounding both to 7+5 or rounding to one decimal place? Explain briefly.
rounding to one decimal yields better 6.8+5.0=11.8 vs 7+5=12
Explain how the commutative and associative properties help when adding three decimals mentally. Show with numbers.
You can move around the numbers and the addends to make it easier to add
Sam saved $12.50 in January, $8.75 in February, and $15.60in March. How much did he save in total? Then estimate the total by rounding each month to the nearest dollar.
exact $36.85; estimated $13+9+16=$38
A store sold 3.45 yards of fabric and then 7.125 yards.
How many yards in all?
10.575
A recipe calls for 2.75 liters of milk. You have 5.6 liters. How much milk is left after making the recipe twice? (Show subtraction steps.)
Start with 5.6−2.75=2.85.6−2.75 = 2.85 for one recipe, twice uses 5.5 so left 0.10
estimate whether 48.765+12.239 is closer to 60 or 61. Explain your
48.765 + 12.239≈60.999→61
Use the terms "compatible numbers", "commutative property", and "associative property" in one sentence that explains a strategy for estimating the sum of 14.9+0.11+5.01
When I estimate I can use the communitive property to switch the numbers orders and the associative property to regroup the numbers to use compatible numbers to get the sum of 21.
A bakery used 7.325 kg of flour on Monday and 9.48 kg on Tuesday. They had 20 kg at the start of the week. After those two days, how much remains? Show exact subtraction and then check the reasonableness using estimation.
exact remainder 20.00−(7.325+9.48)=3.195