Critical Reasoning

please solve

The general availability of high-quality electronic scanners and color printers for computers has made the counterfeiting of checks much easier. In order to deter such counterfeiting, several banks plan to issue to their corporate customers checks that contain dots too small to be accurately duplicated by any electronic scanner currently available; when such checks are scanned and printed, the dots seem to blend together in such a way that the word "VOID" appears on the check.

A questionable assumption of the plan is that:

A. In the territory served by the banks the proportion of counterfeit checks that are made using electronic scanners has remained approximately constant over the past few years.
B. Most counterfeiters who use electronic scanners counterfeit checks only for relatively large amounts of money.
C. The smallest dots on the proposed checks cannot be distinguished visually except under strong magnification.
D. Most corporations served by these banks will not have to pay more for the new checks than for traditional checks.
E. The size of the smallest dots that generally available electronic scanners are able to reproduce accurately will not decrease significantly in the near future.

When doing critical reasoning problems, it's best to read the question first. In this case, the question asks us to identify a questionable assumption. Before we can do so, we must find the conclusion.

When a plan is presented, we can often approximate the conclusion as "The plan will succeed" or "The plan will reach its goal."

The goal of the plan is to deter check counterfeiting. The plan is to put small dots on checks issued to corporate customers that contain dots too small for current technology to properly reproduce.

One way to determine that you have the correct assumption is the negation test. The correct assumption will, if negated, disprove the conclusion.

Let's imagine that we are trying to decide between C and E. The negation test can help us. Let's look at the negated version of C.

(C) The smallest dots on the proposed checks can be distinguished visually without the need for strong magnification.

Does this weaken the conclusion? Not at all. The point of the plan is that scanners will cause these dots to form the word VOID not that people won't be able to see the dots themselves.

(E) The size of the smallest dots that generally available electronic scanners are able to reproduce accurately will decrease significantly in the near future.

Does this weaken the conclusion? Absolutely! If new scanners are on the horizon that will be able to copy these checks without producing the telltale VOID mark, then the plan will fail.