What is the best way to use mental math to multiply (5x18)x20?
well, 5 x 20 = 100
and 100 x 18 = 1800
To use mental math to multiply (5x18)x20, you can break down the problem step by step.
First, multiply 5 by 18. To do this mentally, you can use the distributive property as follows:
5x18 = 5x(10+8) = 5x10 + 5x8
Now multiply each part separately. 5x10 is easy to calculate mentally as 50. To multiply 5 by 8 mentally, you can use a shortcut by multiplying 5 by 2 and then multiplying the result by 4.
5x2 = 10
10x4 = 40
So, 5x8 is equal to 40.
Now, we have 5x18 = 50 + 40 = 90.
Next, multiply the result (90) by 20. To do this mentally, multiply 9 by 20 and then add a 0 at the end.
9x20 = 180
So, (5x18)x20 is equal to 1800.
Therefore, the best way to use mental math to multiply (5x18)x20 is to break down the problem into smaller, more manageable steps and use shortcuts whenever possible.