Question

A student writes, "the difference between 15 and the product of 5 and y" to describe the expression 5y-15. Explain the error

Answer 1

The student should have phrased it to be "the difference between the product of 5 and y and 15", as the way the student writes it implies that 5y is being subtracted from 15 instead of the other way around. 

Answer 2

Answer with explanation:

The expression is given by:

" The difference between 15 and the product of 5 and y "

This means that the product of 5 and y is subtracted from 15.

Now, the product of 5 and y is given by: 5y

and when it is subtracted from 15 then the resulting expression is given by:

                         15-5y

but the student gave the expression as:

                            5y-15

i.e. he subtracted 15 from the product of 5 and y.