Mental Math
Estimating Sums and Differences
Addition
Subtraction
Suprise Catagoy
100
Use mental math to solve 11 + 7
18 (10 + 7= 17 + 1 = 18)
100
Round to the highest place value, then solve. 35 +44 ----------
80 (40+40)
100
82 + 17 -----------
99
100
63 - 51 ---------
12
100
The word DIFFERENCE in a math problem means to complete which math operation?
Subtraction
200
Use mental math to solve 22 + 5
27 (20 + 5 = 25 + 2 = 27)
200
Round to the highest place value, then solve. 83-48
30 (80-50)
200
126+212
338
200
396-125
271
200
Would you need an exact answer or an estimate in the following problem? Sally sold 845 ice cream cones and Henry sold 221 more ice cream cones than Sally. About how many were sold altogether?
Estimate
300
Use mental math to solve 58 + 3
61 (Take 2 away from the 3 and add it to 58 to get 60, 60 + 1 left over = 61)
300
Round to the highest place value, then solve. 860+140
1000 (900+100)
300
77 +73 ---------
150
300
45,822 - 11,974 ------------------
33,848
300
84,694 +72,831 -----------------
157,525
400
Use mental math to solve...Pedro sold 104 double-dip ice cream cones. Carrie sold 75 double-dip cones. How many double-dip ice cream cones did they sell in all?
179 double-dip ice cream cones (100 + 75 = 175 + 4 more = 179)
400
Round to the highest place value, then solve. 859-723
200 (900-700)
400
1,554+7,968
9,522
400
There were 321,025 people that asked for chocolate ice cream. Then 205,776 people asked for strawberry ice cream. How many fewer peopl asked for strawberry than chocolate ice cream?
115,249 people
400
Decide if you need an exact answer or estimate and solve. On Thursday, 15,396 gallons of milk were used. On Friday, 18,709 gallons of milk were used. About how many more gallons were used on Friday than on Thursday?
Estimate: 4,000 gallons (19,000-15,000)
500
Use mental math to solve...In the morning, Tommy made 448 chocolate shakes. In the afternoon he made 50 shakes. How many more shakes did he make in the morning? What is the answer and explain how to use mental math to solve.
398 more shakes (450-50=400-2=398)
500
Round to the highest place value, then solve. Lucy sold 3,486 ice cream cones in one month. Pete sold 8,430 ice cream cones in the same month. How many ice cream cones were sold altogether?
11,000 ice cream cones (3,000+8,000)
500
On Sunday, 14,672 people bought ice cream. On Monday, 25,539 bought ice cream. How many people bought ice cream altogether?
40,211 people
500
36,002,108 - 28,472,510
7,529,598
500
Solve this problem...Sally sold 845 ice cream cones and Henry sold 221 more ice cream cones than Sally. About how many were sold altogether?
1,800 ice cream cones (800+200=1000, 800+1000=1,800)
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