Multiplying decimal values and whole numbers is pretty simple. You just have to learn where to put the decimal point. Here's an example:
70 * .7 = 49
7 * 7 = 49 70 * 7 = 490 70 * .7 = 49 7 * .7 = 4.9
80 * .8 = 64 90 * .5 = 45 30 * .4 = 12 20 * .9 = 18
Now you get to try a few for yourself.