Technically, that is true. One year for the Old Testament and one year for the New Testament. That makes two years. The Book of Mormon is studied for one year. That’s one year. So technically speaking, the Bible is studied “twice as long” as the Book of Mormon is studied. In that one class. However, those studies are part of a four-year cycle, not a three-year cycle. During the remaining year of the four year circuit, Mormons study the exclusively Mormon “Doctrine and Covenants” and “Pearl of Great Price” and Church History. All in all, for that adult class then, the Bible is studied one half as much as Mormon scriptures (and Mormon history). The weekday morning classes for Mormon high school students focus on the same subjects in much the same proportions.
There are other classes, too, regularly attended by many of the same people who attend that four-year cycle of classes. If we include them, then the Christian Bible is studied less than half as much as Mormon additions. For example, this year in the men’s Melchizedek Priesthood class and the women’s Relief Society class, if the lds org page I read is correct, the subject of study is the teachings of Howard W. Hunter. The young men’s class (Aaronic Priesthood) is studying Mormon doctrines, for which specific Bible passages are occasionally used.
In routine class, the Bible is referred to roughly as much as the Book of Mormon, and the Doctrine and Covenants and Pearl of Great Price are referred to usually a bit less than is the Book of Mormon. So although the Bible *is *used, is referred to often, and *is *a subject of specific study for two years out of four in the adult Sunday School class, it is studied less than half as much as uniquely Mormon scriptures, doctrines, and sermons of Mormon leaders.
By virtue of the Mormon Church’s 8th Article of Faith - “We believe the Bible to be the word of God as far as it is translated correctly; we also believe the Book of Mormon to be the word of God.” - the Book of Mormon takes precedence over the Bible. The Book of Mormon is identified as “the word of God.” The Bible, however, is limited according to the accuracy of the translation used - only “as far as it is translated correctly” and no further. I find this odd, since the Bible is available in the form of ancient writings in original languages, but the Book of Mormon exists only in translation! Nowhere are the original documents to be found to compare the accuracy of the translation. It would make more sense, for Christians and non-Christians alike, were the 8th Article of Faith to read, "We believe the Bible in the original Hebrew, Aramaic and Greek to be the word of God; we also believe the Book of Mormon to be the word of God as far as it is translated correctly."
Mormon Prophet Boyd K. Packer taught that one purpose of the Book of Mormon is to explain the Bible, the Bible and apostles themselves apparently being deficient in this task: “I love this Book of Mormon: Another Testament of Jesus Christ. Study it and one can understand both the Old Testament and the New Testament in the Bible.” Apparently, he believes that anyone who does not study the Book of Mormon cannot understand either the Old Testament or the New. In the missionary manual, “Preach My Gospel,” Mormons are taught, “Use the Book of Mormon to clarify and explain Bible passages.” From speaking with Mormons, attending Mormon classes, and reading Mormon literature, I understand that most Mormons believe the Book of Mormon is superior to (since it clarifies, explains, and expands on) the Bible in its doctrinal inerrancy, historical accuracy, clarity, persuasiveness, and explanatory power.
