Multiple numbers that are close to 100 with this method. For this example example, multiply 95 x 81.
Subtract each number from 100. 100 - 95 = 5 and 100 - 81 = 19.
Arrange the numbers from Step 1 in the following manner:
95 5
81 19
Subtract crosswise either (95 - 19) or (81 - 5) to get 76, which is the first part of the answer. Then multiply vertically 19 X 5 = 95, which is the second part of the answer. The final answer is 7695.
Multiply numbers, which are just over 100, such as 105 X 103, by following Steps 2 through 4. For this example, you get:
105 5
103 3
Add crosswise either (105 + 3) or (103 + 5) to get 108. Then multiply vertically (5 x 3) to get 15. The final answer is 10815. Note that for numbers over 100, you add crosswise. For numbers just below 100 you have to subtract crosswise.
Multiply this example: 24 X 41. Imagine that 41 is directly below 24:
24
41
Start from the bottom right and multiply 4 X 1 = 4.
Multiply crosswise 1 X 2 = 2 and 4 X 4 = 16.
Add 2+16 = 18 from Step 3. Put down 8 and carry 1 over.
Multiply vertically 2 X 4 = 8 and add the carried over 1, so 8 + 1 = 9. The final answer is 984. You can use this method to solve long multiplications of any size. With practice, you'll be able to do these calculations mentally.