Estimation
estimate this sum: 79.1 + 32.4
80 + 32 = 112 (I rounded 79.1 to 80 to make the addition quicker)
add: 72 + 3.67
75.67 (line up the decimal point & use place holder zeros!)
subtract: 7.8 - 4.9
2.9
Describe when you round a value up and down
if the number to the right of the place to which you are rounding is 5 or greater, round up!
if the number to the right is less than 5, the value stays the same.
estimate the difference: 418.5 - 23.7
420-24=396 (I rounded 418.5 to 420 to be a larger, round number. mentally, I quickly subtracted 420-20 to get 400. then I compensated for the 4 I took away from 24 and got 396)
Explain how you would add 26.35 + 7.6
Line up the numbers with like place value. this can be easier to do with graph paper. You might focus on the decimal points and use place holder zeros:
26.35
+7.60
33.95
subtract: 65 - 23.98
41.02 (use place holder zeros and line up the decimals!)
Name this Property: you can add numbers in any order
Ex: $11.45 + $3.39 = $3.39 + $11.45
Commutative Property
textbook, page 52, question 21
1017 - 843 = 1020 - 840 = 180 acres
on page 60 in textbook: answer question 13
82.6 pounds
subtract: $10.05 - $4.50
$5.55
a term for numbers that are easy to compute mentally:
You might estimate 339 + 468 to 350 + 450 because they are easy to add = 800
compatible numbers
page 52, #20
it is better to estimate a lesser number that can be seated on the bus. I would estimate each bus seats 45 students. that is a round number to work with. then if you need an extra spot for bags or equipment, if a student feels sick...there is more than enough space.
in textbook on page 60: answer question 14
Macon, GA and Springfield, MO,
if I estimate, 20-2 = 18...this defies the rules of rounding, but it does give me a ballpark figure to see that the decimal is in the wrong place: 1.8 vs 18..ooops!
Explain how to use a bar diagram to answer this question: Luz Maria had $15. She buys a ticket to a movie and a smoothie. How much money does she have left? (the pricing guide is on page 67 in the textbook.)
You could mark the bar with $15. Then draw a box for the ticket ($9.50) and another box for the smoothie ($2.85). If you add $9.50 + $2.85, you get $12.35. That means there is an "empty box" left in the bar...$15 = $12.35 =$2.65 is how much she has left
page 52, question 19
Ed's estimate is slightly higher. He likely rounded $16.98 to $17 and $9.29 up to $10. $10 + $17 = $27. He rounded up on both values, when traditional rules of rounding would suggest you round $9.29 to $9
on page 60, answer question #16
($17.50 + $16) - ($8.50 + $1.95) = $23.05
on page 64 in the textbook, answer #30
Jonah has $92.05 in his bank account...to make it at least $100, he needs $7.95 more deposited into his bank account
How could you use compensation to subtract 12.3 - 4.9
adjust one or both numbers to make the calculation easier, then adjust the difference or sum to get the final answer most accurate:
you could + .1 to 4.9 to = 5
12.3-5 = 7.3...then add the .1 you added and get 7.4