how do you know where to put a decimal point on a product?

Example

5.305 x  .0005

Multiply this without the decimals...so we have

5305 x 5 = 26525

Note that the (understood) decimal  is after the last '5'

Count the number of total decimal places in the two original numbers = 7

Move the understood decimal to the left 7 places (adding zeros, if necessary !!)....so we have...

.0026525

Hope that helps....