Let the probability of showing an even number be \( P \). According to the question, the probability of showing an odd number is \( 3P \). From the total probability: \[ 3P + P = 1 \] Solving: \[ P = \frac{1}{4}, \quad 3P = \frac{3}{4} \] Now, the sum of the numbers in two throws is even when either both numbers are odd or both are even. The required probability: \[ = \frac{3}{4} \times \frac{3}{4} + \frac{1}{4} \times \frac{1}{4} \] \[ = \frac{9}{16} + \frac{1}{16} = \frac{10}{16} = \frac{5}{8} \]