Question

in a computer game there are builders and destroyers. together there are 25 of them. the builder try to build a wall around a castel while destroyer try to demolish it.each of the builders can build the wall alone in 20 hrs while any of the destroyers can demolish it in 15 hrs. if all tha 25 made them active when there is no wall and the wall gets build in 5 hrs, how many of them are destroyers?

Answer 1

Answer:

9 Destroyers are there

Step-by-step explanation:

Destroyer + Builder = 25

Let say Number of builders = B

Then Number of destroyer = 25 - B

1 Builder can build wall in 20 hrs

in 1 hr  1 builder can built wall  = 1/20

B builders in 1 hr can build wall in B/20

B builders in 5 hr can build wall in 5B/20  = B/4

1 Destroyer  can demolish wall in 15 hrs

in 1 hr 1 destroyer can demolish wall  = 1/15

25-B destroyers in 1 hr can demolish wall  = (25 - B)/15

25-B destroyers in 5 hrs  can demolish a  wall in  5(25-B)/15  =  (25-B)/3

B/4  - (25-B)/3  = 1

multiplying by 12 both sides

=> 3B - 100 + 4B = 12

=> 7B = 112

=> B = 16

16 Builders are there

25-16 = 9 Destroyers are there