Sakshi can do a piece of work in 20 days. Tanya is 25% more efficient than Sakshi. The number of days taken by Tanya to do the same piece of work is:

Let 1 man's 1 day's work = x and 1 boy's 1 day's work = y.

Then, 6x + 8y =	1	and 26x + 48y =	1	.
	10		2

Solving these two equations, we get : x =	1	and y =	1	.
	100		200

(15 men + 20 boy)'s 1 day's work =	❨	15	+	20	❩	=	1	.
		100		200			4

∴ 15 men and 20 boys can do the work in 4 days.

Suppose A, B and C take x,	x	and	x	days respectively to finish the work.
	2		3

Then,	❨	1	+	2	+	3	❩	=	1
		x		x		x			2

⟹	6	=	1
	x		2

⟹ x = 12.

So, B takes (12/2) = 6 days to finish the work.

Ratio of rates of working of A and B = 2 : 1.

So, ratio of times taken = 1 : 2.

B's 1 day's work =	1	.
	12

∴ A's 1 day's work =	1	; (2 times of B's work)
	6

(A + B)'s 1 day's work =	❨	1	+	1	❩	=	3	=	1	.
		6		12			12		4

So, A and B together can finish the work in 4 days.

1 woman's 1 day's work =	1
	70

1 child's 1 day's work =	1
	140

(5 women + 10 children)'s day's work =	❨	5	+	10	❩	=	❨	1	+	1	❩	=	1
		70		140				14		14			7

∴ 5 women and 10 children will complete the work in 7 days.

(P + Q + R)'s 1 hour's work =	❨	1	+	1	+	1	❩	=	37	.
		8		10		12			120

Work done by P, Q and R in 2 hours =	❨	37	x 2	❩	=	37	.
		120				60

Remaining work =	❨	1 -	37	❩	=	23	.
			60			60

(Q + R)'s 1 hour's work =	❨	1	+	1	❩	=	11	.
		10		12			60

Now,	11	work is done by Q and R in 1 hour.
	60

So,	23	work will be done by Q and R in	❨	60	x	23	❩	=	23	hours ≈ 2 hours.
	60			11		60			11

So, the work will be finished approximately 2 hours after 11 A.M., i.e., around 1 P.M.

B's 10 day's work =	❨	1	x 10	❩	=	2	.
		15				3

Remaining work =	❨	1 -	2	❩	=	1	.
			3			3

Now,	1	work is done by A in 1 day.
	18

∴	1	work is done by A in	❨	18 x	1	❩	= 6 days.
	3				3

Let A's 1 day's work = x and B's 1 day's work = y.

Then, x + y =	1	and 16x + 44y = 1.
	30

Solving these two equations, we get: x =	1	and y =	1
	60		60

∴ B's 1 day's work =	1	.
	60

Hence, B alone shall finish the whole work in 60 days.

Formula: If A can do a piece of work in n days, then A's 1 day's work =	1	.
	n

(A + B + C)'s 1 day's work =	❨	1	+	1	+	1	❩	=	7	.
		24		6		12			24

Formula: If A's 1 day's work =	1	,	then A can finish the work in n days.
	n

So, all the three together will complete the job in	❨	24	❩ days	=	3	3	days.
		7				7

(B + C)'s 1 day's work =	❨	1	+	1	❩	=	7	.
		9		12			36

Work done by B and C in 3 days =	❨	7	x 3	❩	=	7	.
		36				12

Remaining work =	❨	1 -	7	❩	=	5	.
			12			12

Now,	1	work is done by A in 1 day.
	24

So,	5	work is done by A in	❨	24 x	5	❩	= 10 days.
	12				12

A's 1 hour's work =	1	;
	4

(B + C)'s 1 hour's work =	1	;
	3

(A + C)'s 1 hour's work =	1	.
	2

(A + B + C)'s 1 hour's work =	❨	1	+	1	❩	=	7	.
		4		3			12

B's 1 hour's work =	❨	7	-	1	❩	=	1	.
		12		2			12

∴ B alone will take 12 hours to do the work.