Let the required number of days be x.

Less persons, More days (Indirect Proportion)

More working hours per day, Less days (Indirect Proportion)

Persons	30	:	39		:: 12 : x
Working hours/day	6	:	5

30 x 6 x x = 39 x 5 x 12

x =	(39 x 5 x 12)
	(30 x 6)

x = 13.

After 10 days : 150 men had food for 35 days.

Suppose 125 men had food for x days.

Now, Less men, More days (Indirect Proportion)

125 : 150 :: 35 : x       125 x x = 150 x 35

x =	150 x 35
	125

x = 42.

Let the required number of bottles be x.

More machines, More bottles (Direct Proportion)

More minutes, More bottles (Direct Proportion)

Machines	6	:	10		:: 270 : x
Time (in minutes)	1	:	4

6 x 1 x x = 10 x 4 x 270

x =	(10 x 4 x 270)
	(6)

x = 1800.

Cost of x metres = Rs. d.

Cost of 1 metre = Rs.		d
		x

Cost of y metres = Rs.		d	. y		= Rs.		yd	.
		x					x

Let the required number of working hours per day be x.

More pumps, Less working hours per day (Indirect Proportion)

Less days, More working hours per day (Indirect Proportion)

Pumps	4	:	3		:: 8 : x
Days	1	:	2

4 x 1 x x = 3 x 2 x 8

x =	(3 x 2 x 8)
	(4)

x = 12.