# Engineering Maths - Time and Work

>>>>>>>>Time and Work

• Option : C
• Explanation : When A runs 5 rounds, B runs 4 rounds (ratio of speeds)
A passes B each time A has run 5 rounds or 5 x 1/4 = 5/4km. = 1 1/4km
1 1/4km is contained in 4 km 3 times. Hence A passes B thrice.

• Option : D
• Explanation :
Total area to be painted
= 10 x 15 (ceiling) + 2 x 10 x 10 (wall) + 2 x 10 x 15 (wall)
= 650 sq.ft
In one day Meera can paint 10 x 10/2 = 50 sq ft
Ashok can paint 10 x 10/3 = 100/3 sq ft,
So, together they can paint 250/3 sq ft per day.
Let number of days Ashok works be x.
Work done in 9 days = 50(9 - x) + (250/3)x = 650
∴ 450 - 50x + (250x/3) = 650
⇒ 250x/3 = 200
⇒ x = 6 days.

• Option : A
• Explanation :
Let fixed interval be x

⇒ (5)6 + (5 - x)4 + (5 - 2x)3 = 60
⇒ 30 + 20 - 4x + 15 - 6x = 60
⇒ x = hour.

• Option : C
• Explanation :
Let pipe B alone take b hours longer than if both A and B were open.
8 = √(4 × x)
⇒ 64 = 4 × x
⇒ x = 16 hours.
Alternatively
Part filled if both A and B are open = 1/8
Part filled if only A is open = 1/12
∴ Part filled if only B is open = (1/8) - (1/12) = 1/24
∴ B alone would take 24 hours, i.e., B alone would take 24 - 8 = 16 hours longer to fill the tank.

• Option : C
• Explanation :
Top tap is operational till 18 litres is drawn out.
∴ Time after which the lower tap is usually open = 18 x 6 = 108 minutes.
∴ Time after which it is open now = 108 - 24 = 84 minutes.
∴ Litres d rawn = 84/16 = 14 litres
∴ 18 - 14 = 4 litres
were drawn by the new assistant.
∴ Time = 4 x 4 = 16 minutes.

Alternatively
Upper tap was not used for 24 minutes.
∴ Litres drawn = 24/6 = 4 litres.
∴ Beer was drawn for 4x 4 = 16 minutes.