3rd Grade - Check Precise Calculations Using Context

 
     
 
     
 
Newsletters:
 
     
 
 
3rd
Reasoning
Check Precise Calculations Using Context
Make precise calculations and check the validity, of the results from the context of the problem.
Mathematical Reasoning: precise calculations, check validity or accuracy, problem solving The ability to calculate answers (add, subtract, multiply or divide without making mistakes) with precision and to check those answers to make sure they make sense.
 

Sample Problems

(1)

What does precise mean? (To add, subtract, multiply or divide without making mistakes; to get an exact answer)

(2)

How do you check that 81 divided by 9 is actually 9? (9 x 9 = 81)

(3)

How do you check that 200 – 150 is 50? (50 + 150 = 200)

(4)

Does it make sense?

Jane bought 6 bags of 10 crackers for her study group. Does she have enough for all 5 people to have eight? (Yes, all four people could have twelve)

(5)

Does it make sense?

Mickey wanted to give Minnie a present for her birthday. He bought her a box of chocolates that cost $20. He paid with a fifty-dollar bill and got a ten and a twenty back. Is that right? (Yes. He got $30 change from $50)

Learning Tips

(1)

Precise calculations” is the mathematical term for “adding, subtracting, multiplying or dividing without making mistakes.”

(2)

Children need to understand that just because they use a calculator to compute results, the answer isn’t necessarily accurate. Sometimes the wrong buttons are pushed by mistake, and if the problem called for subtraction but the child performed an addition operation, the result will be wrong.

(3)

In daily living examples, draw your child’s attention to times when mathematical accuracy is in the child’s best interests. For example, if a mistake is made in adding up the number of cupcakes needed for a party, someone will not get one.

(4)

The context of a word problem often tells you what mathematical operation is needed. Teach your child to look for such words as “altogether” (add or multiply), “difference” or “left over” (subtraction), “groups of” (probably indicates one factor in a multiplication operation), “divided up” “shared” (division).

(5)

Teach your child common ways of “proving” answers. In addition, reverse the order of addition (3+4+5 changed to 5+3+4); in subtraction, add the answer and the subtrahend (bottom number in the problem) to see if you get the minuend (top number); in multiplication, reverse the numbers and multiply again (i.e., 34 x 53 can be re-multiplied as 53 x 34 to see if the same answer is obtained. In division, one should get the dividend (the number that is being divided into equal parts) if the divisor (the number of items in each group) is multiplied by the quotient (the answer that was obtained in the original problem.)

Extra Help Problems

(1)

50 + 43 + 76 = ? (169)

(2)

987 – 723 = ? (264)

Check your answer and show your work.

(3)

Divide 232 by 2 and check your work. (116)

(4)

10,432 – 6,555 = ? (3,877)

Check your work.

(5)

8,456 + 777 = ? (9,233)

(6)

900 x 5 = ? (4,500)

(7)

765 x 2 = ? (1,530)

(8)

893 – 43 = ? (850)

(9)

1,025 – 867 = ? (158)

(10)

84 + 23 + 1,896 = ? (2,003)

(11)

How can you check this answer:

When I divide 144 by 12, I got the answer of 12. (12 x 12 = 144)

(12)

How can you check this answer:

96 divided by 3 = 32 (3 x 32 = 96)

(13)

How can you check this answer:

100 divided by 10 = 9 (No, because 10 x 9 = 90)

(14)

How can you check this answer:

82 – 12 = 70 (70 + 12 = 82)

(15)

How can you check this answer:

112 – 23 = 99 (No, because 23 + 99 = 122)

(16)

How can you check this answer:

26 – 13 = 13 (13 + 13 = 26)

(17)

How can you check this answer:

3/8 – 2/8 = 1/8 (1/8 + 2/8 = 3/8)

(18)

How can you check this answer:

.25 - .20 = .05 (.20 + .05 = .25)

(19)

How can you check this answer:

.55 - .50 = .5 (No, .50 + .5 = 1)

(20)

How can you check this answer:

72 divided by 9 = 7 (No, 7 x 9 = 63)

(21)

If three people went to the movies and they each bought tickets for $8.00. I think they spent $25. (They spent exactly $24, but bringing $25 between them would have been a good idea to make sure they had enough money)

(22)

My mom baked three trays of shortbread with 12 cookies on each tray. I want to divide the cookies amongst my Girl Scout troop, which has 8 girls in it. I think they’ll each get 3 cookies and I’m not sure how many I’ll have left over. (No, you can actually give them 4 cookies and you’ll have 4 left over)

(23)

I love to go surfing in the early evening. There were two other girls out there and six big waves. I think we should each get three. Is that fair? (Yes.)

(24)

I want to get 100 problems right on my test, but I only got ¾ of them right. I got 75 problems right. (Yes.)

(25)

How many problems did I miss? 30? (No, 25)

newsletters

 

Related Games

 
 

Copyright ©2009 Big Purple Hippos, LLC