How to multiply 7.86 and 4.6

When you multiply decimals you do NOT need to worry about lining up the decimals. You only need to worry about lining up the decimals when adding or subtracting. 
1) Set up your expression vertically 
7.86
x 4.6

2) Multiply as you would normally
(i.e., 6 x 6 = 36, 6 goes into product, 3 is place above the 8 in the tenths place) 

3) Place the decimal in your product by counting the number of decimal places in each of the factors 
a) 7.86 is in the hundredths place and therefore has 2 decimal places
b) 4.6 is in the tenths place and therefore has 1 decimal place
c) Add the sum of both the factor's decimal places (2+1 = 3)
d) Count out 3 decimal places in the product starting from the right (36156 = 36.156)
e) 36.156 is in the thousandths place, which is correct since the decimal has been placed properly