$5000 grew to $9000 at the compound interest of 12% per annum what was the years taken for the investment​

What is the number 321,000,000 in scientific notation? also what is the number? ?

On a string instrument, the length of a string varies inversely as the frequency of its vibrations. an 11-inch string has a frequency of 400 cylces per second. find the frequency of a 10-icnch string.

If the sales price of a dvd is $20 and the markup is 34%, what is the cost of the dvd?