Mental Math
86+25
90+25=115
Or something reasonable
Estimate by rounding to the nearest 10
542+27
540+30=570
821+4,543
5,364
527-338+
189
810-638=
172
566-359
560-360=200
Or something reasonable
Estimate by rounding to the nearest 10
5,323-2,611
5,320-2,610=2,710
1,321+2,246=
3,567
479-88=
391
7,006-3,529=
3,477
(40+5) + 8=
45+8=53
Estimate by rounding to the nearest 100
5,317+1,734
5,300+1,700=7,000
16,018+135
16,153
8,617-3,909=
4,708
10,807-4,373=
6,434
is 881-262 more or less than 500? Explain how you can tell using mental math
It is more than 500 because if you round both numbers up, the answer is well over 500
Estimate by rounding to the nearest 100
1,724-731
1,700-700=1,000
7,845+509+3,746+
12,100
1,111-589=
522
3,000-1,047=
1,953
An adult human body has a total of 206 bones. There are 300 bones in a child's body because some of a child's bones fuse together as a child grows. How many more bones are there in a child's body than an adult's body?
300-206=94
This year, 35,658 people ran in a marathon. Last year, 8,683 fewer people ran. About how many people ran last year?
36,000-9,000=27,000
15,891+527+1,086+
17,504
7,475-5,130=
2,345
12,000-10,296
1,704