Question

A bricklayer's apprentice takes 10 hours longer than the bricklayer to make a fireplace. The apprentice worked alone on a fireplace for 5 hours, after which the bricklayer began to help. It took 2 more hours for them to finish the fireplace. How long would it take the apprentice to make the fireplace on his own?

Answer 1

It would take the apprentice 14 hours to make the fireplace on his own.

Explanation:

Let x represent the hours it takes the bricklayer to make a fireplace on his own and x + 10 represent the hours it takes the bricklayer's apprentice to make a fireplace on his own.

7/(x + 10) + 2/x = 1

7/(x+10) represents the fraction of the fireplace the bricklayer's apprentice made (total amount of time the bricklayer's apprentice worked on the fireplace/time it takes the bricklayer's apprentice to make a fire place on his own) while 2/x represents the fraction of the fireplace the bricklayer made (total amount of time the bricklayer worked on the fireplace/time it takes the bricklayer to make a fire place on his own). The 1 on the right side of the equation represents the number of fireplaces they made in that time.

Multiply both sides of the equation by x(x + 10) to get rid of the denominators:

x(x + 10)[7/(x + 10) + 2/x] = x(x + 10)1

x(x + 10)[7/(x + 10)] + x(x + 10)(2/x) = x(x + 10)

7x + 2(x + 10) = x² + 10x

7x + 2x + 20 = x² + 10x

Gather all the terms to one side of the equation:

x² + 10x - 7x - 2x - 20 = 0

x² + x - 20 = 0

Factoring the simplified equation:

(x + 5)(x - 4) = 0

Solving for each factor:

When x + 5 = 0,

x = -5

When x - 4 = 0,

x = 4

Since a negative solution wouldn't make sense for this question, it would take the bricklayer 4 hours to complete the fireplace on his own.

Substituting x = 4 into x + 10 to find out how long it would take the apprentice to make the fireplace on his own:

x + 10 = 4 + 10 = 14

Therefore, it would take the apprentice 14 hours to make the fireplace on his own.