Mental Math
How could you add these numbers mentally?
275 + 180 + 120 =
80 + 20 = 100 so 180 + 120 = 200. Then add 200 + 275 = 475
Estimate by rounding to the nearest whole.
19.7 - 6.9 =
20 - 7 = 13
55.25 + 2.98 + 16.3 =
74.53
82.7 - 5.59
77.11
0.5 is 10 times as great as ____
0.005
How can you add these numbers mentally?
7.35 + 1.47 + 9.65 =
.35 + .65 = 1.00 so 7. 35 + 9.63 = 17.00. Then add 17.00 + 1.47 = 18.47.
Estimate by rounding to the nearest whole.
5.82 + 1.69 + 2.3 =
6 + 2 + 2 = 10
37.2 + 103.0 + 8.52 =
143.72
6.04 - 3.48
2.56
0.002 is 1/10 of _____
0.02
Jerome is buying school supplies. He buy's a notebook for $2.55, pencils for $1.45, and an eraser for $0.75. Use mental math to find how much he spent in all.
$.55 and $.45 = $1 so $2.55 + $1.45 = $4.00. $4.00 + $.75 = $4.75
Estimate by rounding to the nearest whole.
87.99 - 52.46
88 - 52= 36
88.8 + 4.27 + 78.95 =
172.02
$72.35 - $6.19
$66.16
0.08 is 10 as great at ___.
0.008
In a week Danika ran 8.7 miles and Anthony ran 6.8 miles. Use mental math to find how much farther Danika ran than Anthony. Explain.
If you subtract 0.1 from 6.8 then 8.7 - 6.7 = 2. If I subtract the 0.1 from 2 my answer will be 1.9.
8.7- 6.8 = 1.9
Carol bought an orange for $0.89 and a soda for $1.95. Which is the best estimate of how much she spent?
A. $2.00
B. $3.00
C. $4.00
D. $5.00
A
Reilly adds 46.3 and 2.21. Should his sum be greater than or less than 48. How do you know?
Greater; When adding the whole numbers only the sum is 48 so if you add the whole decimal the sum will be greater than 48.
Which two problems have a difference of 10.2?
12.05 -2.03
16.29 - 6.09
36.1 - 25.9
22.09 - 21.07
10.82- 9.8
16.29 - 6.09
36.1 - 25.9
0.01 is 10 as great as ___
0.001
How is using mental math to add with decimals like using mental math to add with whole numbers?
You still use the same properties of addition and compatible numbers.
A gardener is estimating how much topsoil is needed for a small vegetable garden. Is it better to estimate a greater or lesser amount than he needs? Why?
Greater; to make sure he has enough to plant his vegetable gardern.
Choose all the expressions that are equal to 15.02.
A. 12.96 + 2.06
B. 0.56 + 14.64
C. 2.62 + 12.4
D. 1.22 + 1.8 + 12
E. 1. + 0.5 + 13. 8
A, C, D
The annual rainfall in Albany is 46.92. This is 0.33 inch less than Nashville . Miami has an annual rainfall of 61.05. How much less rainfall does Nashville get than Miami?
13.80
0.1 is 10 times as great as ___
0.01