What is an a priori proposition? an a posteriori proposition?

Sam opened a money-market account that pays 3% simple interest. he started the account with $7,000 and made no further deposits. when he closed the account, he had earned $420 in interest. how long did he keep his account open?

Measure a and b and find their sum. how are the angles related?

Use a standard normal table to determine the probability. give your answer as a decimal to four decimal places. −1.5< < 1.5)