Answer: 1/2
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To do this problem, you'll have to subtract fractions. To subtract fractions, find a common denominator on both fractions (if needed, which you don't need to do for this problem!), subtract the numerators, and put the difference over the common denominator. Simplify if needed.
Ella started out with 7/10 a bucket of water and then lost 2/10 by pouring it out. That means you're finding the difference of 7/10 - 2/10!
1) Find a common denominatorThis is already done because both fractions have "10" in the denominator.
2) Subtract the numerators7 and 2 are the numerators and you're subtracting 2 from 7:
7 - 2 = 5
3) Put the difference of the numerators over the common denominator

4) Simplify if needed

This is because you can divide both the numerator and denominator by 5/5 (and remember 5/5 is the same as 1, and dividing any number by 1 equals itself!)