pushpitkc wrote:

In the first consignment, 12% bulbs were faulty. In the second consignment, 4% bulbs were faulty.

In the two consignments, 7% bulbs were faulty. If the two consignments combined had 4000 bulbs,

how many faulty bulbs did the first consignment have?

A. 60

B. 100

C. 175

D. 180

E. 300

Source:

Experts GlobalWeighted average, in which

\(x\) = number of bulbs in first consignment

\(4000 - x\) = number of bulbs in second consignment

\(.12(x) + .04(4000-x) = .07(4000)\)

\(.12x + 160 -.04x = 280\)

\(.08x = 120\)

\(x = \frac{120}{.08}=\frac{12000}{8}=1500\)

\(x\) is the number of bulbs in first consignment.

\(12\) percent are faulty

\(12\) percent of \(1500\) is

\(180\)

Answer D

The formula I used.

(%) = percent faulty

A = consignment #1

B = consignment #2

(% A)(# of A) + (% B)(# of B) = (% of A+B)(# of A+B)
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