Two different types of alloy, a and b, have been used to manufacture experimental specimens of a small tension link to be used in a certain engineering application.
theultimate strength (ksi) of each specimen was determined, and the results are summarized inthe accompanying frequency distribution

ab[26,30)73[30,34)129[34,38)1519[38 ,42)710 total 4141

compute a 95% ci for the difference between the true proportions of all specimens of alloysa and b that have an ultimate strength of at least 34 ksi.