Chain Rule

Question: A flagstaff 17.5 m high casts a shadow of length 40.25 m. The height of the building, which casts a shadow of length 28.75 m under similar conditions will be:

[A].

10 m

[B].

12.5 m

[C].

17.5 m

[D].

21.25 m

Answer: Option B

Explanation:

Let the height of the building x metres.

Less lengthy shadow, Less in the height (Direct Proportion)

40.25 : 28.75 :: 17.5 : x       40.25 x x = 28.75 x 17.5

x =	28.75 x 17.5
	40.25

x = 12.5

Question:
An industrial loom weaves 0.128 metres of cloth every second. Approximately, how many seconds will it take for the loom to weave 25 metres of cloth?

[A].

178

[B].

195

[C].

204

[D].

488

Answer: Option B

Explanation:

Le the required time be x seconds.

More metres, More time (Direct Proportion)

0.128 : 25 :: 1 : x       0.128x = 25 x 1

x =	25	=	25 x 1000
	0.128		128

x = 195.31.

Required time = 195 sec (approximately).

Question:
If a quarter kg of potato costs 60 paise, how many paise will 200 gm cost?

[A].

48 paise

[B].

54 paise

[C].

56 paise

[D].

72 paise

Answer: Option A

Explanation:

Let the required weight be x kg.

Less weight, Less cost (Direct Proportion)

250 : 200 :: 60 : x       250 x x = (200 x 60)

x=	(200 x 60)
	250

x = 48.

Question: If the cost of x metres of wire is d rupees, then what is the cost of y metres of wire at the same rate?
[A].

Rs.		xy
		d

[B].

Rs. (xd)

[C].

Rs. (yd)

[D].

Rs.		yd
		x

Answer: Option D

Explanation:

Cost of x metres = Rs. d.

Cost of 1 metre = Rs.		d
		x

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