WIth a ratio of 20/82 you want it in terms of 155.
For every 82 units you have 20. So similar to when you calculate a percentage (in terms of 100) you can do the same method here.
\({20 \over 82} = {20 \over 82} * {155 \over 155} = {20 * 155 \over 82} * {1\over 155} = {37.8 * {1\over155}} = {37.8\over 155}\)
37.8 here is rounded, not exact.
