To find out how much longer the yellow gold necklace is than the white gold necklace, we can subtract the length of the white gold necklace from the length of the yellow gold necklace.
The lengths are as follows:
- White gold necklace: 16.4 inches
- Yellow gold necklace: 18.26 inches
Now, we perform the subtraction:
\[ 18.26 \text{ inches} - 16.4 \text{ inches} = 1.86 \text{ inches} \]
Therefore, the yellow gold necklace is 1.86 inches longer than the white gold necklace.