Latest self Aptitude Question SOLUTION: Jack and Danny are bricklayers. Jack can build a certain brick wall in 8 hours whereas Danny takes 11 hours. If they work together, their combined rate decreases by 7 bricks an hou

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(#M40020949) SELF question Keep an EYE

Jack and Danny are bricklayers. Jack can build a certain brick wall in 8 hours whereas Danny takes 11 hours. If they work together, their combined rate decreases by 7 bricks an hour, and it only takes them 5 hours to build the wall together. Find the number of bricks in the wall

k.d.n padma rao (10 years ago)

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Vaibhav Mishra  (10 years ago)

let the number of brick in the wall be x

jack can lay x bricks in 8 hrs => x/8 bricks per hour
danny can lay x bricks in 11 hrs => x/11 bricks per hour

combined rate = x/8 + x/11 bricks per hour

working together causes their combined rate to decrease by 7 bricks per hour

combined rate while working together = x/8 + x/11 - 7 bricks per hour

it takes them 5 hours to build the wall

5*(x/8 + x/11 - 7) = x

expand the brackets

5x/8 + 5x/11 - 35 = x

now solve it by multiply both sides by 88

55x + 40x - 3080 = 88x

95x - 88x = 3080

7x = 3080

x = 440...so the number of bricks will be 440

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