87. A necklace is made by stringing N individual beads
together in the repeating pattern red bead, green
bead, white bead, blue bead, and yellow bead. If the
necklace design begins with a red bead and ends with
a white bead, then N could equal
(A) 16
(B) 32
(C) 4 1
(D) 54
(E) 68
答案是E,这是OG的解释：
Algebra Applied problems
Th e bead pattern repeats after every fifth bead.
Since the first bead in this design (or the first in
the pattern) is red and the last bead in this design
(or third in the pattern) is white, the number of
beads in this design is 3 more than some multiple
of 5. Th is can be expressed as 5n + 3, where n is
an integer. Test each of the answer choices to
determine which is a multiple of 5 plus a value
of 3. Of the options, only 68 = 5(13) + 3 can be
written in the form 5n + 3.
问题：
1、(or third in the pattern) is white 白色不是排最后嘛？怎么又变成第三了?
2、the number of
beads in this design is 3 more than some multiple
of 5. 这话咋理解呢~~~~~~
3、5n + 3 这又是咋回事呢~~~~~~~
