Question

the nrr, or noise - reduction rating, is the number of db subtracted from a workers noise exposure. for instance, if a worker using a circular saw (90 db) wears earplugs with an nrr of 20 db, his total exposure is 70 db (90 - 20 = 70). suppose you are working with equipment that produces 120 db of noise. several different protective devices are shown below, along with their noise - reduction ratings. which one should you wear in order to bring your noise exposure down to 90 db or less? select your answer by pressing the letter. a) disposable foam earplugs (nrr 14) b) reusable pvc earplugs (nrr 14) c) general - purpose earmuffs (nrr 23) d) custom - molded earplugs (nrr 33)

Explanation:

Step1: Determine the required NRR

The equipment produces 120 dB of noise and we want the exposure to be 90 dB or less. Let the NRR be $x$. We use the formula: Noise exposure = Original noise - NRR. So, $120 - x\leq90$.

Step2: Solve for x

Rearrange the inequality $120 - x\leq90$. First, subtract 120 from both sides: $-x\leq90 - 120$, which simplifies to $-x\leq - 30$. Multiply both sides by - 1 (and reverse the inequality sign), we get $x\geq30$.

Answer:

D. Custom - molded earplugs (NRR 33)