Respuesta :

Story:

Karina had 7 notebooks. He sister left for her some more notebooks, but Karina did not check how many.

Later she counted, and she had 9 notebooks.

How many notebooks did her sister leave for her?

and the solution:

7+x=9

we subtract 7 from both sides:

7-7+x=9-7

now we calculate what we can:

x=2

so the solution is: she left two notebooks.
if K.C. has 7 tablets and her mom and dad get her sister, liz,  2 tablets how many tablets would her and her sister have?
          7+   =9                      9-7= 2
                           9 is the whole
                     7 is how many K.C. has
                       2 is how many liz has
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