4 men and 6 boys can do a piece of work in 20 days. It is also done by 3 men and 4 boys in 28 days. How long would it take for one man or one boy to it?
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let the work done my 1 man be X and the work done by 1 boy be y
4/X+6/y =1/20. ×4
3/X+4/y=1/28. ×6
16/X+24/y=1/5
18/X+24/y=3/14
(-) (-) (-)
____________
-2/X =1/5-3/14
=14-15/14
=-1/14
2/X=1/14
X=28
4/28+6/y=1/20
1/20-4/28=6/Y
7-20/28=6/y
-14/28=6/y
-1/2=6/y
y=-12
4/X+6/y =1/20. ×4
3/X+4/y=1/28. ×6
16/X+24/y=1/5
18/X+24/y=3/14
(-) (-) (-)
____________
-2/X =1/5-3/14
=14-15/14
=-1/14
2/X=1/14
X=28
4/28+6/y=1/20
1/20-4/28=6/Y
7-20/28=6/y
-14/28=6/y
-1/2=6/y
y=-12
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