t₁=8+t₂
S=160

160/2v₁=160/v₂+3
160/v₁=160/v₂+8

80/v₁=160/v₂+3
160/v₁=160/v₂+8 {(-)

80/v₁=5
v₁=80/5=16km/h.

160/v₂=160/v₁-8=10-8=2
v₂=160/2=80km/h

5 adults == 12 days.
1 adults == 12/5 days.

1 adults 1 days = 1/(5*12)=1/60

12 children completed a work of 18 days.
1 child = 18/12 days.

1 child’ 1 days = 1/(18*12)=1/216

10 adults working 2 days =>
2•10•1/60=1/3

1-1/3=2/3 left to do.

Now we have 4 children and (10-8) adults==>
2/60+4/216=1/30+1/54=14/270=7/135

2/3•1/(7/135)=135/7•2/3=90/7

Ans A

Plzz bta do koi

Any shortcut?

bc=-a(b+c)
ab=-c(b+a)
ac=-b(a+c)

a²/(a²-bc)+b²/(b²-ac)+c²/(c²-ab)=
a²/(a²+a(b+c))+b²/(b²+b(a+c))+c²/(c²+c(b+a))=
a/(a+b+c)+b/(a+b+c)+c/(a+b+c)=
(a+b+c)/(a+b+c)=1