Question

A and B can do a piece of work in 72 days. B and C in 120 day and A and C in 90day In what time can A alone do it ​

Answer 1

Answer:

A+B=72

B+C=120

A+C=90

Now by subtracting

(A+C)-(B+C)=A-B

90-120=-30

then adding

(A+B)+(A-B)=2A

72-30=42

A=21

Answer 2

Answer:

A and B can do a piece of work in 72 days, B and C in 120 days, A and C in 90 days so the total work = LCM of 72, 90 and 120 = 360 work .

A and B are doing in one day = 360 / 72 = 5

B and C are doing in 1 day = 360/90 = 4

A and C are doing in 1 day = 360/120= 3

5+4+3= 12

2(a+b+c)

12/2=6

(a+b+c)

360/6= 60

a+b = 5

6-5=1

c=1

b+c=4

b=4-1=3

a= 2

if A do 2 work in a day so 360 work will be done in days = 360/2=180 days

Ans... 180 days