If x=0.2, then what is the value of x^3-1/x-1?

[Max@Math Revolution]

[GMAT math practice question]

If x=0.2, then what is the value of x^3-1/x-1?

A. 1.2
B. 1.22
C. 1.24
D. 1.44
E. 2.22

[Brent@GMATPrepNow]

[GMAT math practice question]

If x=0.2, then what is the value of x^3-1/x-1?

A. 1.2
B. 1.22
C. 1.24
D. 1.44
E. 2.22

Some spaces and/or brackets would definitely help here.
Do you mean x^3 - 1/x - 1 or x^3 - 1/(x - 1) or (x^3 - 1)/(x - 1)??

Cheers,
Brent

[Scott@TargetTestPrep]

[GMAT math practice question]

If x=0.2, then what is the value of x^3-1/x-1?

A. 1.2
B. 1.22
C. 1.24
D. 1.44
E. 2.22

((0.2)^3 - 1)/(0.2 - 1)

(0.008 - 1)/(-0.8)

(-0.992)/(-0.8) = 1.24

Alternate solution:

The formula for factoring the difference of cubes is (x^3 - 1) = (x - 1)(x^2 + x +1). We can use that fact to simplify (x^3 - 1)/(x - 1) = x^2 + x + 1. Therefore, when x = 0.2, we have:

(0.2)^2 + 0.2 + 1 = 0.04 + 0.2 + 1 = 1.24

Answer: C

[Max@Math Revolution]

=>

$$\frac{x^3-1}{x-1}=\frac{\left(x-1\right)\left(x^2+x+1\right)}{x-1}=x^2+x+1$$

Plugging in x = 0.2 yields
x^2+x+1 = (0.2)^2 + (0.2) + 1 = 0.04 + 0.2 + 1 = 1.24

Therefore, the answer is C.
Answer: C