Question

Ms. Lim asked her class to find an expression equivalent to 7 - 3 (4 - 2x) - 10x .

whats wrong with these problems? please include your work.

Answer 1

Solving
`7-3(4-2x)-10x` we get
`-4x-5`

Explanation:

Jon solved:

7-3(4-2x)-10x

4(4-2x)-10x

16-8x-10x

16-18x

Error in John Work

The error in John work is that he subtracted 7-3 first, which is wrong. According to the rule, first brackets are solved, then multiplication or division and then addition or subtraction is performed.

Madison Solved:

7-3(4-2x)-10x

7-3(2x)-10x

7-6x-10x

7-16x

Error in Madison Work

The error in Madison work is that she subtracted (4-2x) and get 2x which is wrong. Only like terms are added or subtracted. 4 and -2x are not like terms so, we can't subtract them

Selina Solved:

7-3(4-2x)-10x

7-12-2x-10x

-7-12x

Error in Selina Work

The error in Selina work is that she wrongly multiplied -3 with -2x

-3(-2x) we get 6x but Selina found it to be -2x which is wrong.

My solution:

Now, we will solve the equation correctly

`7-3(4-2x)-10x`

First, multiply -3 with terms inside the bracket

`7-12+6x-10x`

Now, combine like terms

`7-12+6x-10x\\-5-4x`

or we can write -4x-5

So, solving
`7-3(4-2x)-10x` we get
`-4x-5`