3 years ago sum of ages of all 5 members was 80 years
And average was 16 year
At present sum of ages of all 5 members and age of baby(x) is
80+(3*5)+x=95+x
Average at present is
(95+x)/6 =16(Given)
95+x=96
X=96-95=1
Hence age of baby is=x=1 year
A does 1/6 of work in one day
B does 1/12 of same work in one day
Both of them does (1/6)+(1/12)=1/4 of work in one day
Let x be the time taken by both of them to do the whole work
So they will take
(1*x)/4=1
From here
X=4 days
Both of them will take 4 days to complete the work
4/5-3/4=1/20
Here value of 5 litre water is 1/20
Then
Let x be the capacity of tank
So
(1*x)/20=5
X/20=5
And from here,
X=100 litre
Capacity of tank is 100 litre
(c) 100