To find out how much cookie is left after Mary and Peter ate, we need to add the portions they ate and subtract that sum from the whole cookie (1 whole cookie).
Mary ate \( \frac{3}{10} \) and Peter ate \( \frac{4}{10} \).
Now, let's add the amounts they ate:
\[ \frac{3}{10} + \frac{4}{10} = \frac{7}{10} \]
Now we subtract the total amount they ate from 1 whole cookie:
\[ 1 - \frac{7}{10} = \frac{10}{10} - \frac{7}{10} = \frac{3}{10} \]
So, the remaining amount of cookie is \( \frac{3}{10} \).
Since this value does not appear in your provided options, the answer you might be looking for was found incorrectly. The remaining amount is \( \frac{3}{10} \).
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