Abhijit K wrote:If two copying machines work simultaneously at their constant rates, how many copies do they produce in 5 minutes?
1.One of the machines produces copies at the constant rate of 250 copies per minute.
2.One of the machines produces copies at twice the constant rate of the other machine.

Please help with approach.

This one's a little tricky in that it seems to provide enough information without actually doing so.

To answer the question we need either the individual rate of each machine, or the rate of the machines working together. So let's see if either their individual rates or their rate working together can be found using the statements.

Statement 1 give us the rate of one of the machines but not that of the other. Without both rates we can't calculate their production. So Statement 1 is insufficient.

Statement 2 gives us only their relative rates and no way to get from that to their actual rates. So Statement 2 is insufficient.

Now comes the trick. We have the rate of one machine from Statement 1, and from Statement 2 we know that one machine works twice as fast as the other. So the temptation is to think that we can use the rate we have and either multiply or divide by 2 to get the other rate, but that won't work. We don't know whether 250 copies per minute is the rate of the faster machine or that of the slower machine, and there is no clue we can use to figure that out.

So even combined the Statements do not provide information sufficient for determining the answer.

Choose E.