Bunuel wrote:

Tough and Tricky questions: Word Problems.

One out of every 1000 computer chips is defective. If 2 out of every 30 defective chips have defective processors and there are 30 defective processors in the first batch, how many computer chips are there in the first batch?

A. 450

B. 900

C. 90,000

D. 450,000

E. 900,000

Kudos for a correct solution.I thought of this question as a set within a set, which prevented me from choosing trap answer A.

Let D = number of defective parts generally

Let P = number of defective parts with bad processors (P is a subset of D)

Let T be total number of chips

**Quote:**

One out of every 1000 computer chips is defective.

\(\frac{D}{T}=\frac{1}{1000}\)

**Quote:**

If 2 out of every 30 defective chips have defective processors

\(\frac{2}{30}\) or\(\frac{1}{15}\)D are P, or P = \(\frac{1}{15}\)D

**Quote:**

there are 30 defective PROCESSORS in the first batch

P = 30, substitute that value:

30 = \(\frac{1}{15}\)D

D = 450 in the first batch

**Quote:**

how many computer chips are there in the first batch?

\(\frac{D}{T}=\frac{1}{1000}\)

\(\frac{450}{T}=\frac{1}{1000}\)

T = 450,000

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