Convert 0.31 to binary then back to base 10 and work out the error

The size of a certain cell is 2.5*10^-9m. another cell is 1.5*10^3 times larger. how large is the larger cell in scientific notation?

Erin bought christmas cards for $2 each to send to her family and friends. which variable is the dependent variable?

Two cities a and b are 1400km apart and lie on the same n-s line. the latitude of city a is 23 degrees. what is the latitude of city b. the radius of the earth is approximately 6400km.