Question

Working alone, it would take Shandra 40 minutes to sand a table. To sand the same table, also working alone, it would take Kelly 1 hour. If they work together, the situation can be modeled by the following equation, where t is the time it would take to sand the table working together.

Shandra claims it will take them about 50 minutes working together, because 50 is the mean of 40 and 60. Which best describes Shandra’s claim?

Shandra’s claim is correct.

Shandra’s estimate is too high because she should have found the differences instead of the mean.

Shandra’s estimate is too high because it will take them about 24 minutes.

Shandra’s estimate is too low because it will take them about 100 minutes.

​

Answer 1

Answer:

The third option is the best description.

Step-by-step explanation:

Shandra needs 40 minutes to complete to sand the table.

In 1 minute,  Shandra completes $\frac{1}{40}$ part of the work.

Similarly, Kelly takes 1 hour, that is 60 minutes to complete to complete the work.

In 1 minute, Kelly completes $\frac{1}{60}$ part of the work.

In 1 minute, they together completes $\frac{1}{40} + \frac{1}{60} = \frac{40 + 60}{40\times60} = \frac{100}{240} = \frac{5}{12}$ part of the work.

Hence, $\frac{5}{12}$ part of the work takes 1 minute to complete.

The whole work will be completed in $\frac{12}{5}$ = 2 minute 24 seconds.

Shandra’s estimate is too high because it will take them about 2 minutes 24 seconds.

Answer 2

Answer: Shandra’s estimate is too high because it will take them about 24 minutes.

Step-by-step explanation: Edg 2020