If (a+b)=7, ab=11, then (a-b)=?


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Deborah Mann Profile
Deborah Mann answered
  • The answer

There are two potential answers to this question; (a - b) could either equal two point two or minus two point two.

  • How this is worked out

To begin with, we need to consider what two numbers, when added together, give an answer of 7, something which does not take very long to work out: 2 plus 5 will give 7, as would 4 and 3.

The next step is to see which of these two options would, when multiplied together, give an answer of 11.

We can see that 4 multiplied with 3 is 12, and that 2, when multiplied with 5, gives 10, meaning that neither of these two options can equal a and b.

It is because of this, then, that we need to think about going into decimal figures; as 5 x 2 gives the closest answer to 11, it will be this set of digits that we need to play around with.

Using your calculator will help, as this is just a simple tactic of trial and error, and so would speed things up greatly.

Once you have done this, you should have realized that 4.6 multiplied by 2.4 gives an answer of 11.04, which is the closest that we can get, and therefore close enough.

We now have values for a and b, but unfortunately there is no way of telling which is which, and it is because of this that we gain two different answers.

When 2.4 is taken away from 4.6, we gain an answer of 2.2, which gives us the potential answer of the equation.

When 4.6 is taken from 2.4, we gain an answer minus 2.2, the possibility, and one that is as equally as valid as the first.

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