Question 1145794
Rate of work for A = 1/A job per day
Rate of work for B = 1/B job per day
Rate of work for C = 1/C job per day
<pr>
Rate of work for A, B, and C working together = 1/A + 1/B + 1/C = 1/10
Rate of work for A and B working together = 1/A + 1/B = 1/12
Rate of work for A and C working together = 1/A + 1/C = 1/20
<pr>
1/A + 1/C = 1/20
1/C = 1/20 - 1/A
<pr>
1/A + 1/B = 1/12
1/B = 1/12 - 1/A
<pr>
1/A + 1/B + 1/C = 1/10
1/A = 1/10 - 1/C - 1/B 
1/A = 1/10 - (1/20 - 1/A) - (1/12 - 1/A) 
1/A = 1/10 - 1/20 + 1/A - 1/12 + 1/A
1/A = -1/30 + 2/A
-1/A = -1/30
1/A = 1/30
A = 30
<b>It takes 'A' 30 days to do the job alone.</b>
<pr>
1/A + 1/B = 1/12
1/30 + 1/B = 1/12
1/B = 1/12 - 1/30
1/B = 1/20
B = 20
<b>It takes 'B' 20 days to do the job alone.</b>
<pr>
1/A + 1/C = 1/20
1/30 + 1/C = 1/20
1/C = 1/20 - 1/30
1/C = 1/60
C = 60
<b>It takes 'C' 60 days to do the job alone.</b>