SOLUTION: three skilled laborers a,b,c together can do construction job in 20 days a & b could do the job in 30 days b & c could do the job in 40 dyas. how long would it take each to do the

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Question 224473: three skilled laborers a,b,c together can do construction job in 20 days a & b could do the job in 30 days b & c could do the job in 40 dyas. how long would it take each to do the job alone?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
three skilled laborers a,b,c together can do construction job in 20 days a & b
could do the job in 30 days b & c could do the job in 40 days.
how long would it take each to do the job alone?
:
Write a "shared work" equation for each statement
:
"three skilled laborers a,b,c together can do construction job in 20 days"
Let the completed job = 1.
20%2Fa+%2B+20%2Fb+%2B+20%2Fc = 1
:
" a & b could do the job in 30 days"
30%2Fa+%2B+30%2Fb = 1
:
" b & c could do the job in 40 days"
40%2Fb+%2B+40%2Fc = 1
:
how long would it take each to do the job alone?
:
We can use elimination here:
Multiply the 1st equation by 2, subtract the 3rd equation
40%2Fa+%2B+40%2Fb+%2B+40%2Fc = 2
___40%2Fb+%2B+40%2Fc = 1
--------------------------------
40%2Fa = 1
a = 40 days alone
:
Replace a with 40 in the 2nd equation
30%2F40+%2B+30%2Fb = 1
3%2F4+%2B+30%2Fb = 1
30%2Fb = 1 - 3%2F4
30%2Fb = 1%2F4
multiply both sides by 4b
4(30) = b
b = 120 days alone
:
Find c using the 3nd equation, replace b with 120
40%2F120+%2B+40%2Fc = 1
1%2F3+%2B+40%2Fc = 1
40%2Fc = 1+-+1%2F3
40%2Fc = 2%2F3
Multiply both sides by 3c
3(40) = 2c
120 = 2c
c = 120%2F2
c = 60 days alone
:
Solutions: a = 40 days, b = 120 days, c = 60 days
;
:
Check this using the 1st equation
20%2F40+%2B+20%2F120+%2B+20%2F60 = 1
1%2F2 + 1%2F6 + 2%2F6 = 1