A and B can do a work in 4days, B and C in 5days, C and A in 7days. If A,B and C work together , they will complete the work in? Choose the correct choice from the following:
A) 3days
B) 5days
C) 7days
D) 1days
E) 2dasy
3days+B 1day work = 1/4   B+C 1day work  +  1= 
<gadget id="calculator"> +  1</gadget>
<output>1</output>
1/4   B+C 1day work = 1/5   C+3days 1day work  +  1= 
<gadget id="calculator"> +  1</gadget>
<output>1</output>
1/5   C+3days 1day work= 1/7   3daysdding we get 2(3days+B+C) = 1/4 + 1/5 + 1/7 = 83/140   3days+B+C 1 day work = 83/280   3days,B,C can finish the work in 280/83 days = 3days approximately   3daysnswer is 3days
<result>A</result>
A and B can do a work in 4days, B and C in 5days, C and A in 7days. If A,B and C work together , they will complete the work in?