Carcass wrote:
If 4(2x+1)+4(x+1)=80, what is the value of x ?
(A) -5
(B) 0
(C) 1
(D) 4
(E) 5
STRATEGY: Upon reading any GRE Multiple Choice question, we should always ask, Can I use the answer choices to my advantage?
In this case, we can easily test the answer choices.
In fact, if I apply a little bit of number sense, I can quickly rule out answer choices D and E, since 4(2x+1) and 4(x+1) would each evaluate to be much greater than 80.
From here, I'd typically give myself up to 20 seconds to identify a faster approach, but I can already see that testing the answer choices will be super fast.
Let's start by testing answer choice B,
x=0.
When we plug
x=0 into the given equation we get:
4(2(0)+1)+4(0+1)=80Simplify to get:
41+41=80Evaluate to get:
4+4=80. Doesn't work!
So, we can eliminate answer choice B .
More importantly, we can see that we need the exponents to be bigger in order to get a sum of 80.
So let's now test answer choice C,
x=1.
We get:
4(2(1)+1)+4(1+1)=80Simplify to get:
43+42=80Evaluate to get:
64+16=80Works!!
Answer: C