Write + or - in each \( \bigcirc \) to make each equation true. (a) \( \frac{13}{18} \bigcirc \frac{1}{9} \bigcirc \frac{1}{2} \bigcirc \frac{2}{3}=1 \)

To solve this equation, we need to fill in the \( \bigcirc \) symbols with either \( + \) or \( - \) so that the left side of the equation equals 1. Let's experiment with the combinations. Start with the equation: \[ \frac{13}{18} \bigcirc \frac{1}{9} \bigcirc \frac{1}{2} \bigcirc \frac{2}{3} \] Let's try using \( + \) and \( - \): 1. First combination: \[ \frac{13}{18} + \frac{1}{9} - \frac{1}{2} + \frac{2}{3} \] Calculate each of the fractions in terms of a common denominator (which can be 18): - \( \frac{1}{9} = \frac{2}{18} \) - \( \frac{1}{2} = \frac{9}{18} \) - \( \frac{2}{3} = \frac{12}{18} \) So the equation becomes: \[ \frac{13}{18} + \frac{2}{18} - \frac{9}{18} + \frac{12}{18} \] Now simplify: \[ = \frac{13 + 2 - 9 + 12}{18} = \frac{18}{18} = 1 \] Thus, one possible solution for \( (a) \) would be: \[ \frac{13}{18} + \frac{1}{9} - \frac{1}{2} + \frac{2}{3} = 1 \] The correct sequence is: \[ + , - , + \] So, the filled expression is \( \frac{13}{18} + \frac{1}{9} - \frac{1}{2} + \frac{2}{3} = 1 \).