BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem
TTP OnDemand GMAT Video Course
Featured Course

Target Test Prep GMAT OnDemand

Scott Woodbury-Stewart’s private virtual classroom — 400 hours of master-class video lessons for the GMAT Focus Edition.

  • 715+ score guarantee — highest in the industry (99th percentile)
  • 52 chapters · 1,500+ lessons · 4,000+ practice questions
  • 400 hours of video · 1,500+ instructor-led HD smartboard lessons
  • 300,000+ students accepted to Harvard, Stanford, Wharton, Booth & Sloan & more
  • 24/7 live support + weekly Zoom office hours with GMAT instructors
  • TTP AI Assist — 24/7 AI-powered virtual tutor for instant help
  • 1,200+ flashcards + AI-powered study assistant & daily calendar
  • OnDemand, LiveTeach & GMAT Bootcamp formats available
  • Also: GRE, SAT Math & Executive Assessment courses
  • MBA Admissions Consulting now available
  • 🏆 2025 EdTech Breakthrough Award: Test Prep Solution Provider of the Year
  • 200,000+ students served
  • 5-day free trial — $0 to start, no auto-billing, cancel anytime
★★★★★ 5.0 (559 reviews)
130-pt guarantee
$0 to start then $127/mo
Start Free 5-Day Trial Read 559 Reviews →

A string of 5 different colored light bulbs is wired in such

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Moderator
Posts: 2632
Joined: Sun Oct 29, 2017 2:08 pmFollowed by: 2 members
by AAPL » Wed Sep 19, 2018 4:55 am

Timer

00:00

Answers

A

B

C

D

E

Stats

Difficulty—

e-GMAT

A string of 5 different colored light bulbs is wired in such a way that if any two-consecutive light bulb fails, then entire string fails. If for each individual light bulb, the probability of not failing during time period T is 0.85, what is the probability that the string of light bulbs will fail during the time period T?

A. 0.0225
B. 0.09
C. 0.225
D. 0.25
E. 0.5

OA B.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Problem Solving |
Legendary Member
Posts: 2214
Joined: Fri Mar 02, 2018 2:22 pmFollowed by: 5 members

by deloitte247 » Sun Sep 23, 2018 8:12 am
Given that ;
There is a string of 5 different colored light bulbs.
The string fails if any two consecutive light bulb fails .
The probability of each bulb not failing during a period of time T = 0.85
Question=
Find the probability that the string of light will fail during the period time T.

Answer =
Probability of a bulb not failing = 0.85
Probability of a bulb failing = 0.15
Total ways in which 2 consecutive light bulbs can fail in a string of 5 bulbs = 4
Probability that the string of light bulbs will fail,
= Probability of one bulb fail * Probability o another consecutive bulb fail * ways in which 2 consecutive bulb can fail.
= 0.15 * 0.15 * 4
=0.09
Option B is CORRECT.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 3008
Joined: Mon Aug 22, 2016 6:19 amFollowed by: 34 members
Location: Grand Central / New York
Thanked: 470 times

by Jay@ManhattanReview » Mon Sep 24, 2018 9:37 pm
AAPL wrote:e-GMAT

A string of 5 different colored light bulbs is wired in such a way that if any two-consecutive light bulb fails, then entire string fails. If for each individual light bulb, the probability of not failing during time period T is 0.85, what is the probability that the string of light bulbs will fail during the time period T?

A. 0.0225
B. 0.09
C. 0.225
D. 0.25
E. 0.5

OA B.
The string would fail if 1st and 2nd; 2nd and 3rd; 3rd and 4th; or 4th and 5th bulbs together fail.

Given that the probability of not failing during the time period T is 0.85, we have the probability of failing during the time period T = 1 - 0.85 = 0.15.

1. Probabality of failing of 1st and 2nd bulbs = 0.15 * 0.15 = (0.15)^2;
2. Probabality of failing of 2nd and 3rd bulbs = (0.15)^2;
3. Probabality of failing of 3rd and 4th bulbs = (0.15)^2;
4. Probabality of failing of 4th and 5th bulbs = (0.15)^2

Thus, the probability that the string of light bulbs will fail during the time period T = 4*(0.15)^2 = 4*0.025 = 0.09

The correct answer: B

Hope this helps!

-Jay
_________________
Manhattan Review GMAT Prep

Locations: New York | Paris | Shanghai | Munich | and many more...

Schedule your free consultation with an experienced GMAT Prep Advisor! Click here.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1