35/23 is an improper fraction because the numerator is larger than the denominator.
To convert to a mixed number, use long division to find 35 into 23 goes in exactly one whole time (quotient) and there is 12 leftover (remainder)
You can see it through doing it like this
35/23 = (23+12)/23 = 23/23 + 12/23 = 1 + 12/23 = 1 & 12/23
So in short, 35/23 = 1 & 12/23
1 & 12/23 is a mixed number with 1 as the whole part and 12/23 as the fractional part.
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Real life example: if you had 35 cookies and 23 friends, then each friend would get 1 whole cookie. There would be 12 cookies left over.