a recipe calles for 1 6/8 cups

To convert 1 6/8 cups into a mixed number, we add the whole number 1 and the fractional part 6/8:

1 + 6/8

To simplify the fraction, we can divide both the numerator and denominator by their greatest common factor, which in this case is 2:

1 + 3/4

So, 1 6/8 cups is equivalent to 1 3/4 cups.