A lapping slurry contains microbeads suspended in a solution and is used to polish a silicon wafer by abrasion of the surface. The distribution of the particle size, in micrometers, is shown above. If the particle size distribution ranges were changed to 0-20 micrometers and 21-40 micrometers, which of the following is the closest to the ratio of the number of 0-20 micrometer microbeads to the number of 21-40 micrometer microbeads?
A. 3:01
B. 4:01
C. 5:02
D. 9:01
Answer:B
A lapping slurry contains microbeads suspended in a solution and is used to polish a silicon wafer by abrasion of the surface. The distribution of the particle size, in micrometers, is shown above. If the particle size distribution ranges were changed to 0-20 micrometers and 21-40 micrometers, which of the following is the closest to the ratio of the number of 0-20 micrometer microbeads to the number of 21-40 micrometer microbeads?
A. 3:01 B. 4:01 C. 5:02 D. 9:01
Explanation: B In the new groupings, 79% of the particles are in the 0-20 micrometer grouping (33% + 46% = 79%) and 21% of the particles are in the 21-40 micrometer grouping (16% + 5%) = 21%. That is a ratio of 79:21. Because the question is asking for the closest ratio, round the numbers to get a ratio of 80:20, or 4:1. The correct answer is (B).