Using an Open Array to Model Decimal x Whole Number Multiplication

Here is a screen shot for how you could use an open array to model 18 x 8.7. First you would draw an array based on how many digits are in each factor (ie two digits x two digits would be a 2 x 2 array, 3 digits x 2 digits would be a 3 x 2 array). Then you would separate each factor by place value along the sides of the array, and solve for each cell of the array by multiplying the side lengths of the cells. Finally you would add all of the partial products in each cell together.

Here is one for 56.1 x 23, which is not as nicely color-coded: