An article: "Second Moment Reliability Evaluation vs. Monte Carlo Simulations for Weld Fatigue Strength (Quality and Reliability Engr. Intl., 2012: 887-896)" examines the use of

Use a uniform distribution with a = 0.20 and b = 4.25 for the diameter X of the welds (mm).

a) Find and plot the density function of X.

b) What is the probability that the diameter exceeds 3 mm?

c) What is the probability that the diameter is within 1 mm of the mean diameter?

d) With a satisfying the condition 0.2 < a < a + 1 < 4.5, what is the probability P(a < X < a + 1)?

so a parallelogram is just like a square base times height. multiply 40 and 39 to get 1560 inches.

a triangle is base times height divided by two. so multiply 7.9 and 5 and then divide it by 2 to get 19.75inches.

the kite can be split into two separate triangles and added together to get the total area. 30 x 4 /2 which equals 60. make sure to double it for the two triangles making 120.

not only in mathematics, scientific proof also are required in the other field of science. also maths proofs are of particular structure, containing steps and logics. so proving is like doing science, it is science. that's why it is important to prove. 

an inaccurate proof leads to errors, or stating results that are not accurate.  which wil mess the probelm up you dont want this