True or False?
The idea of this activity is for you to decide whether each of the number sentences below is true or false.
Try not to use written calculations if you can, and if possible, talk to someone else about your ideas.
When you are ready, click below to see the number sentences. (Alternatively, you could download this sheet which contains all the number sentences. You could print it out and cut it up so that each number sentence is separate.)
We would love to hear about your reasoning. How do you know whether a particular number sentence is true or false?
a. 19 + 15 = 34
b. 34 = 19 + 15
c. 19 + 15 = 15 + 19
d. 34 = 34
e. 19 + 15 = 34 + 0
f. 19 + 15 = 0 + 34
g. 34 = 16 + 17
h. 19 + 15 = 21 + 13
i. 19 + 15 = 20 + 16
j. 19 + 15 = 22 + 18
k. 19 + 15 = 34 + 15
l. 15 + 19 = 20 + 14
For a further challenge, take a look at the number sentences below, or on this sheet.
Which are true? Which are false? How do you know?
Are you able to decide without doing any calculating?
a. 346 + 289 = 349 + 286
b. 727 + 581 = 581 + 727
c. 478 - 192 = 480 - 194
d. 831 - 344 = 841 - 334
e. 346 + 289 = 345 + 288
f. 727 + 581 - 581 = 727
g. 831 - 344 + 346 = 831
h. 169 + 672 = 2041
You might like to use the balance interactivity below to help you make decisions, and/or to check your conclusions.
You can use the calculator tool to create one side of a number sentence.
Pressing 'OK' puts that part of the number sentence into a box which you can drag to one side of the balance.
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