Correct Option: A

For the first 10 days 40 men worked.
Now, 40 men can complete the work in 40 days
∴ 1 man will complete the same work in 1600 days

∴ 1 man’s 1 day’s work	1
	1600

∴ Part of work done in first 10 days

=	1
	4

For the next 10 days 35 men worked.
Part of the work done

=	1 × 35 × 10	=	7
	1600		16

For the next 10 days, 30 men worked
Part of the work done

=	30 × 10	=	3
	1600		16

For the next 10 days, 25 men worked. Part of the work done

=	25 × 10	=	5
	1600		32

Similarly, part of the work done by 20 men in next 10 days

=	20 × 10	=	1
	1600		8

Work done in 50 days

=	1	+	7	+	3	+	5	+	1
	4		32		16		32		8

=	8 + 7 + 3 + 5 + 4	=	30	=	15
	32		32		16

∴ Remaining work

= 1 -	15	=	1
	16		16

Now 15 men remain to work 15 men’s 1 day’s work

=	15
	1600

∴ Time taken to complete	1	part of work
	16

=	1600	×	1
	15		16

=	20	= 6	2	days
	3		3

∴ Total time = 50 + 6	2	= 56	2	days
	3		3