High-strength concrete is supposed to have a compressive strength greater than 6,000 pounds per square inch (psi). a certain type of concrete has a mean compressive strength of 7,000 psi, but due to variability in the mixing process it has a standard deviation of 420 psi, assuming a normal distribution.

Answer

given,

greater compressive strength = 6,000 psi

mean compressive strength(μ) = 7000 psi

standard deviation (σ) = 420 psi

P(X < 6000)                                              

Z = - 2.38                    

P(Z<-2.38) = Area to left - 2.38

from Z table                          

P(X < 6000) = P(Z<-2.38) = 0.0087

P(fail) = P(X< 6000) = 0.0087 = 0.87

4 adults and 12 babies

step-by-step explanation:

4 x 7 = 28

12 x 15 = 180

180 + 28 =208

4 x 3 = 12