Although the objects and ratios have changed (from sheep to coins and from 1% lost to 10% lost), the lesson Jesus is teaching is still the same.
Silver coins were commonly worn as ornaments by women in that day. In addition to their monetary worth, the coins were often valuable sentimentally also since many were handed down from generation to generation.
"Coins" can easily be compared to humans in the sense that the value of any coin is related to its inscription or image. Humans are valuable since they are made in the image of God (cf. Gen. 1:26,27)! Even though this woman had nine other silver coins, she knew the value of the one she had lost. The coin was still valuable to her, even though it was essentially worthless until it was found. Likewise a sinner is essentially worthless in that he can render no acceptable service to God (in that lost condition), but he still has intrinsic value as a human, and thus God wants him back.
Compare the phrases in Luke 15:4,8 - "Until he finds it...until she finds it." The determination of the shepherd and the woman can be seen in their efforts to recover what is lost. The woman would light a lamp to help her see better and sweep the house in hopes of finding the coin. She would use every available means to locate the lost coin. The same is true with God. He will employ the Scriptures, the workings of providence, faithful Christians, etc., for the recovering of His lost "coins."
Like the shepherd in the first parable, the woman also would rejoice when that which was lost had been found. She would invite others to celebrate with her.
Luke 15:10 records a wonderful truth from the Lord - "Likewise I say to you that there is joy in the presence of the angels of God over one sinner who repents." We ought to be encouraged in our efforts to reach the lost, knowing that the angels also have an interest in them. Jesus is trying to shame the religious leaders for their murmuring against Him. He is working hard to save the lost when He eats with them and receives them, but the Pharisees and scribes don't care about anyone but themselves!
Dear friends, let us always remember that there are none so worthless that the Lord doesn't still care about them. God will go to great lengths to recover one who is lost for there is nothing more pleasing to Him than the restoration of one who has been lost in sin. Are we diligent enough in our efforts to try to save the lost and restore the erring? Are we more like the shepherd and the woman or the scribes and Pharisees?