Mental Math Tricks by Kevin OConnor - HTML preview

Adding Time

Here is a nice simple way to add hours and minutes together:

 

Let's add 1 hr and 35 minutes and 3 hr 55 minutes together.

What you do is this:
make the 1 hr 35 minutes into one number, which will give us 135 and do the same for the other number, 3 hours 55 minutes, giving us 355

Now you want to add these two numbers together:

135
355
____
490

So we now have a sub total of 490.

 

What you need to do to this and all sub totals is add the time constant of 40.

 

No matter what the hours and minutes are, just add the 40 time constant to the sub total.

 

490 + 40 = 530

 

so we can now see our answer is 5 hrs and 30 minutes! http://www.memorymentor.com/