Show:
2.1
2.2
2.3
2.5
2.6/2.7
100
What is mental math?
Math you can do in your head.
100
Round to the nearest tens. 16
20
100
Estimate the sum of the two numbers. 79 and 32.
80 + 30 = 110 Always round to the greatest place value in estimating!
100
Add. 5, 741 + 31, 018
36, 759
100
Add. 6.9 + 2.8
9.7
200
Why do we use estimation?
To do mental math, to find an answer quickly, to find an answer close the real answer.
200
Round to the nearest tenths. 56.12
56.10
200
Estimate the difference of the two numbers. 51 and 18
50 - 20 = 30. Always round to the greatest place value in estimating!
200
Add. 7, 110 + 499
7, 609
200
Add. 356.2 + 12.45
368.65
300
Use mental math to add or subtract. ROUND FIRST, then add. 21 + 9 + 12
20 + 10 + 10 = 40 Always round to the greatest place value when doing mental math!
300
Round to the nearest hundreds: 4, 526
4, 500
300
Esimate the sum of the two numbers. 2.9 and 3.9
3.0 + 4.0 = 7.0 Always round to the greatest place value in estimating!
300
Subtract. 4, 002 - 3, 765
237
300
Subtract. 16.82 - 5.21
11.61
400
Use mental math to add or subtract. 35 + 46 + 6
40 + 50 + 10 = 100 Always round to the greatest place value when doing mental math!
400
Pretend that the 0 is underlined. Round. 930, 998
931, 000
400
Estimate the difference of the two numbers. 12.99 and 3.95
13.00 - 4.00 = 9.00 Always round to the greatest place value in estimating!
400
Subtract. 58, 005 - 1, 098
56, 907
400
Subtract. 7.21 - 6.1
1.11
500
Use mental math to add or subtract. 468 - 190.
500 - 200 = 300. Always round to the greatest place value when doing mental math!
500
Pretend that the 4 is underlined. Round. 0.472
0.500
500
Esimate the sum and difference of the two numbers. 77.11 and 8.18
Sum: 80 + 8 = 88 Difference: 80 - 8 = 72
500
Subtract. 103, 558 - 64, 671
38, 887
500
56.8-2.765
54.035