necklace bead colors

[kobel51]

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) 41
D) 54
E) 68

[Patrick_GMATFix]

the pattern repeats itself after every five terms (red, green white, blue, yellow, red...) so if we start with a red, the last yellow bead will be the 5th, 10th, 15th, 20th... bead (a multiple of five) and the white bead that follows must be a multiple of 5 + 3 (8th, 13th, 18th, 23nd...). Only answer E makes sense. The full solution below is taken from the GMATFix App.



-Patrick

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Hi kobel51,

These types of "repeating sequence" questions tend to be easy to beat IF you draw a picture. We're given the repeating sequence of beads: RGWBY...RGWBY...

We're asked if a string starts with R and ends with W, then the total number of beads COULD be. The phrase "could be" is important because it means that there's more than one correct answer. We have to work until we find the correct answer that's listed OR we deduce the pattern.

Following the given rules, at the minimum, we'd have...

RGW = 3 beads

That answer's not there, so keep going with the pattern:

RGWBY
RGW = 8 beads

That answer's not there either, so keep going:

RGWBY
RGWBY
RGW = 13 beads

Now, that answer isn't there either, but we now KNOW the pattern. The total increases by 5 each time, and the correct answer will end in either a 3 or an 8.

Final Answer: E

GMAT assassins aren't born, they're made,
Rich

[rairavig]

since it ends up at white, which is 3rd bead. we can make the equation as:-
3+5n= Ans
any option with unit didgit as 3 or 8 will b the Ans
i belive the right Ans is (E)