Question

Sandra says that 4/7 - 1/3 = 3/4 because all you have to do is subtract the numerators and subtract the denominators. Convince Sandra that she is wrong. You may draw a rectangular fraction model to support your thinking.

Answer 1

She is wrong and the correct answer is
`(5)/(21)`.

Explanation:

The given expression is

`(4)/(7)-(1)/(3)`

Sandra says that
`(4)/(7)-(1)/(3)=(3)/(4)` because all you have to do is subtract the numerators and subtract the denominators.

She is wrong. The correct method is shown below.

Make the denominator common.

`(4* 3)/(7* 3)-(1* 7)/(3* 7)`

`(12)/(21)-(7)/(21)`

On further simplification we get

`(12-7)/(21)`

`(5)/(21)`

Therefore, the correct answer is
`(5)/(21)`.