MemoryMentor’s Blog

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

Let’s add 1 hr and 35 mins and 3 hr 55 mins together.

What you do is this:
make the 1 hr 35 mins into one number, which will give us 135 and do the same for the other number 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 mins are ( as long as they add up to over 60) , 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 mins!

If we wanted to add 1hour 10 mins and 1hour 20mins we would do this:

110 + 120

Sub total would be 230 but adding 40 here would not work. For this to work, the tens part (in this case the 30) needs to be 60 or above as 60 and above is a new hour).