Model 1 Basics On Time & Work Section-Wise Topic Notes With Detailed Explanation And Example Questions
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The following question based on Time & Work topic of Quantitative Aptitude
(a) 3·25 hours
(b) 2·5 hours
(c) 3 hours
(d) 2 hours
The correct answers to the above question in:
Answer: (d)
(A + B)’s 1 hour’s work = $2/9$ .....(i)
(B + C)’s 1 hour’s work = $1/3$ ......(ii)
(C + A)’s 1 hour’s work = $4/9$ .....(iii)
Adding all three equations,
2 (A + B + C)’s 1 hour’s work = $2/9 + 1/3 + 4/9$
${2 + 3 + 4}/9$ = 1
A, B and C together will complete the work in 2 hours.
Using Rule 5,
Time taken = ${2 × 9/2 × 3 × 9/4}/{9/2 × 3 + 3 × 9/4 + 9/2 × 9/4}$
= ${{18 × 27}/8}/{27/2 + 27/4 + 81/8}$
= ${18 × 27}/8 × 8/({108 + 54 + 81})$
= ${18 × 27}/243$ = 2 hours
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Read more basics on time and work Based Quantitative Aptitude Questions and Answers
Question : 1
A and B can do a piece of work in 10 days, B and C in 15 days and C and A in 20 days. C alone can do the work in :
a) 30 days
b) 80 days
c) 60 days
d) 120 days
Answer »Answer: (d)
According to the question
Work done by A and B together in one day = $1/10$ part
Work done by B and C together in one day = $1/15$ part
Work done by C and A together in one day = $1/20$ part
So, A + B = $1/10$ ....(I)
B + C = $1/15$ ...(II)
C + A = $1/20$ ....(III)
Adding I, II, III, we get
2 (A + B + C) = $1/10 + 1/15 + 1/20$
2 (A + B + C) = ${6 + 4 + 3}/60 = 13/60$
A + B + C = $13/120$ ....(IV)
Putting the value of eqn. (I) in eqn. (IV)
$1/10 + C =13/120$
C = $13/120 - 1/10 = {13 - 12}/120 = 1/120$
Work done in 1 day by C is $1/120$ part
Hence, C will finish the whole work in 120 days
Using Rule 19A and B can do a work in 'x' days, B and C can do the same work in 'y' days. C and A can do the same work in 'z' days. Then, all can do alone the work as following:A alone can do in =${2xyz}/{xy + yz - zx}$daysB alone can do in =${2xyz}/{-xy + yz + zx}$daysC alone can do in =${2xyz}/{xy - yz + zx}$days
Time Taken by C= ${2xyz}/{xy - yz + zx}$
= ${2 × 10 × 15 × 20}/{10 × 15 - 15 × 20 + 20 × 10 }$
= $6000/{150 - 300 + 200} = 6000/50$ = 120 days
Question : 2
A and B together can complete a piece of work in 18 days, B and C in 24 days and A and C in 36 days. In how many days, will all of them together complete the work ?
a) 10 days
b) 12 days
c) 16 days
d) 15 days
Answer »Answer: (c)
(A + B)’s 1 day’s work = $1/18$
(B + C)’s 1 day’s work = $1/24$
(A + C)’s 1 day’s work = $1/36$
Adding all three,
2 (A + B + C)’s 1 day’s work= $1/18 + 1/24 + 1/36$
= ${4 + 3 + 2}/72 = 1/8$
(A + B + C)’ 1 day’s work = $1/16$
A, B and C together will complete the work in 16 days.
Using Rule 5,
Total time taken = ${2 × 18 × 24 × 36}/{18 × 24 +24 × 36 + 36 × 18}$
= ${36 × 24 × 36}/{432 + 864 + 648}$
= $31104/1944$ = 16 days
Question : 3
A and B together can do a work in 8 days, B and C together in 6 days while C and A together in 10 days, if they all work together, the work will be completed in :
a) 4$4/9$ days
b) 5$5/47$ days
c) 3$3/4$ days
d) 3$3/7$ days
Answer »Answer: (b)
(A + B)'s 1 day's work = $1/8$ ...(i)
(B + C)'s 1 day's work = $1/6$ ...(ii)
(C + A)'s 1 day's work = $1/10$ ...(iii)
On adding,
2(A + B + C)'s 1 day's work = $1/8 + 1/6 + 1/10$
= ${15 + 20 + 12}/120 = 47/120$
(A + B + C)'s 1 day’s work= $47/240$
(A + B + C) together will complete the work in
$240/47 = 5{5}/47$ days.
Using Rule 5,
Time taken = ${2 × 8 × 6 × 10}/{8 × 6 + 6 × 10 + 10 × 8}$
= $960/{48 + 60 + 80} = 960/188$
= $240/47 = 5{5}/47$ days
Question : 4
A and B can do a piece of work in 12 days, B and C in 8 days and C and A in 6 days. How long would B take to do the same work alone ?
a) 48 days
b) 40 days
c) 24 days
d) 32 days
Answer »Answer: (a)
(A + B)'s 1 day's work = $1/12$ ...(i)
(B + C)'s 1 day's work = $1/8$ ...(ii)
(C + A)'s 1 day's work = $1/6$ ...(iii)
On adding,
2(A + B + C)'s 1 day's work = $1/12 + 1/8 + 1/6$
= ${2 + 3 + 4}/24 = 9/24$
(A+ B + C)'s 1 day’s work = $9/{24 × 2} = 9/48$ ...(iv)
On, subtracting (iii) from (iv),
B’s 1 day’s work = $9/48 - 1/6$
= ${9 - 8}/48 = 1/48$
B can complete the work in 48 days.
Using Rule 19,
B alone can do in = ${2 × 12 × 8 × 6}/{-12 × 8 + 8 × 6 + 6 × 12}$
= ${24 × 48}/{-96 + 48 + 72} = {24 × 48}/{-96 + 120}$
= ${24 × 48}/24$ = 48 days
Question : 5
If A and B together can complete a work in 12 days, B and C together in 15 days and C and A together in 20 days, then B alone can complete the work in
a) 20 days
b) 24 days
c) 30 days
d) 25 days
Answer »Answer: (a)
(A + B)’s 1 day’s work = $1/12$
(B + C)’s 1 day’s work = $1/15$
(C + A)’s 1 day’s work = $1/20$
On adding,
2 (A + B + C)’s 1 day's work = $1/12 + 1/15 + 1/20$
= ${5 + 4 + 3}/60 = 1/5$
(A+B+C)’s 1 day’s work = $1/10$
B’s 1 day’s work = $1/10 - 1/20 = {2 - 1}/20 = 1/20$
B alone can do the work in 20 days.
Using Rule 19,
B alone can do in = ${2 × 12 × 15 × 20}/{-12 × 15 + 15 × 20 + 20 × 12}$
= ${24 × 300}/{-180 + 300 + 240} = {24 × 300}/360$ = 20 days
Question : 6
If A and B together can complete a piece of work in 15 days and B alone in 20 days, in how many days can A alone complete the work ?
a) 30 days
b) 40 days
c) 60 days
d) 45 days
Answer »Answer: (c)
(A + B)’s 1 day’s work = $1/15$
B’s 1 day’s work = $1/20$
A’s 1 day’s work = $1/15 - 1/20 = {4 - 3}/60 = 1/60$
A alone will do the work in 60 days.
Using Rule 4,
A alone do in = ${15 × 20}/{20 - 15}$
= ${15 × 20}/5$ = 60 days
Time & Work Shortcuts and Techniques with Examples
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Model 1 Basics on Time & Work
Defination & Shortcuts … -
Model 2 Formula method ‘M1D1W1 = M2D2W2’
Defination & Shortcuts … -
Model 3 Man leaves & joins
Defination & Shortcuts … -
Model 4 Working with Man, Woman, Child
Defination & Shortcuts … -
Model 5 Split & Fraction of work
Defination & Shortcuts … -
Model 6 Efficiency of the worker
Defination & Shortcuts … -
Model 7 Working with individual wages
Defination & Shortcuts …
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