Twice the difference of 9 and a number.

Explanation:

Difference indicates subtraction:

The difference of a number and

9

is

(

x

−

9

)

Twice the difference means

2

(

x

−

9

)

We know that the answer to this is

2

, so as an equation:

2

(

x

−

9

)

=

2

If you solve it we would have:

x

−

9

=

1

←

÷

2

x

=

1

+

9

x

=

10

The difference between

10

and

9

is

1

and twice

1

is

2

.

The number is correct.

Note that written as:

The difference of twice a number and

9

would have a different expression. This would be

2

x

−

9

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7. d. 64

8. i. 32

9. c. 125

10. j. none of the above

11. d. 81

12. i. 216

13. e. none of the above

14. g. 240

15. e. none of the above

16. g. 32

17.   e. none of the above