(d) Assume that the average life of a refrigerator is 15 years, with the standard deviation given in part (a) before it breaks. Suppose that a company guarantees refrigerators and will replace a refrigerator that breaks while under guarantee with a new one. However, the company does not want to replace more than 10% of the refrigerators under guarantee. For how long should the guarantee be made (rounded to the nearest tenth of a year)

19.1 years

Step-by-step explanation:

Average life of refrigerator = 15 years

lets assume standard deviation = 2.5

The company does not want to replace more than 10%

Determine how long the Guarantee issued by the company should last

since the  company doesn't want the replacement to exceed 10%

we will use the Z score corresponding to ( 100 - 10 ) = 90%

Z score = 1.645

The number of years

= 1.645 * std + 15

= (1.645 * 2.5 ) + 15 = 19.1125 ≈ 19.1 years

tip $2.90

total $17.40