Mental Math

Transcript

Mental Math Mental math is the ability to perform calculations in your head without using a calculator or paper Let’s look at the example of our book What can you say about the numbers and the lines drawn? We note that 38,800 = 25,000 + 400 × 2 + 13,000 3400 = 1500 + 1500 + 400 Now, some more questions Can we make 1,000 using the numbers in the middle? Why not? What about 14,000, 15,000 and 16,000? Yes, it is possible. Explore how. What thousands cannot be made? Now, its important to note that you have to do these without using pen and paper. Here’s how we can do it Can we make 1,000 using the numbers in the middle? Why not? No. The smallest number you can use is 400. You can add it (400 + 400 = 800) or add it again (800 + 400 = 1200), but you can't land exactly on 1,000. No combination of the other numbers helps either. What about 14,000, 15,000 and 16,000? Yes, it is possible. This is where the rule "use as many times as needed" is important. To make 14,000, you can add 400 thirty-five times (400 x 35 = 14,000). To make 15,000, you can add 1,500 ten times (1,500 x 10 = 15,000). To make 16,000, you can add 400 forty times (400 x 40 = 16,000).