Question

Suppose it takes 45 hours for robot A to construct a new robot. Working together with robot B, it takes 25 hours for both robots to construct a new robot. How long would it take robot B to construct a new robot, working alone

Answer 1

Answer:

56 hours 25 minutes

Step-by-step explanation:

Answer 2

Answer:

56 hours 25 minutes

Step-by-step explanation:

Given:

Suppose it takes 45 hours for robot A to construct a new robot

It takes 25 hours for both robots to construct a new robot.

Question asked:

How long would it take robot B to construct a new robot, working alone ?

Solution:

Let the time taken by robot B to construct new robot = $x$

By robot A

It takes 45 hours to construct = 1 new robot

It takes 1 hour to construct = $\frac{1}{45} \ new\ robot$

By robot B

It takes $x$ hours to construct = 1 new robot

It takes 1 hour to construct = $\frac{1}{x}$ new robot

By working together

It takes 25 hours to construct = 1 new robot

It takes 1 hour to construct = $\frac{1}{25} \ new\ robot$

$\frac{1}{25}$ new robot is constructed in = 1 hour

New robot is constructed by both working together in 1 hour = New robot is constructed by robot A in 1 hour + New robot is constructed by robot B in 1 hour

$\frac{1}{25} =\frac{1}{45} +\frac{1}{x}$

Subtracting both sides by $\frac{1}{45}$

$\frac{1}{25}-\frac{1}{45} =\frac{1}{45} -\frac{1}{45}+\frac{1}{x} \\\\\frac{1}{25}-\frac{1}{45} =\frac{1}{x}\\\\ Taking\ LCM \ of \ 25\ and\ 45,\ we\ got\ 225$

$\frac{9-5}{225} =\frac{1}{x} \\ \\ \frac{4}{225} =\frac{1}{x}\\\\ By\ cross \ multiplication\\4\times x=225\\Dividing\ both\ sides\ by\ 4\\x=56.25\ hours$

Thus, robot B would take 56 hours 25 minutes to construct a new robot, working alone.