What it is like scoring 55% in SSLC during late 70s in K'taka

Recently I found some old marks card of our family members. The total % in SSLC are around 50% to 60% for different members of the family, lets consider average as 55%. They all completed SSLC in late 70s. I'm curious to know how it was scoring 55% back then ? Can we compare it to 80% ish for today?