Dropping Common Zeros (again)

I’m excited you’re here with me for Lesson 7, where we’re exploring more ways to subtract in our heads by dropping common zeros—and even using additional shortcuts. Let’s get started!

Sometimes, you’ll see subtraction problems like 90 - 50 and think, “Oh, that’s no problem,” because they’re both multiples of 10. There’s actually a handy shortcut: just drop the zero at the end of each number and subtract the front digits first.

For instance:

• 90 - 50
• If we drop the zero from both, we get 9 - 5 = 4.
• Then we add the zero back, giving us 40.

It’s quick and easy! Essentially, when both numbers end in the same number of zeros, you can ignore those zeros momentarily to subtract the “front digits,” then bring the zeros back at the end. This approach prevents mistakes and speeds up your mental math.

Multiple Shortcuts, Same Result
It’s important to remember there might be more than one way to do the same problem in your head. Let’s look at 860 - 300. Here are two different shortcuts you could use:

• Shortcut 1:View 860 as 86 with one zero at the end.View 300 as 30 with one zero at the end.So, 86 - 30 = 56.Put the zero back, and you get 560.
• Shortcut 2:Think of 860 as 800 + 60.Think of 300 as 300.Start by subtracting the “hundreds” part: 800 - 300 = 500.Then remember the + 60 left from 860, which gives 500 + 60 = 560.

Both methods lead to the same answer, 560. It’s just a matter of which mental approach feels simpler or more natural to you.

Try both ways on your own, and see which shortcut you prefer. Maybe you’ll discover a slightly different way—that’s perfectly fine! The most important thing is using a strategy that keeps the process clear in your mind.

Practice Problems
Now that we’ve seen how to drop zeros and use simple shortcuts, let’s practice. I’ll read each of these problems out loud. After each one, you can pause the podcast, figure out a shortcut, and then resume for the next. Ready?

• 80 - 30
• 800 - 600
• 1400 - 500
• 680 - 200
• 940 - 700
• 590 - 300
• 850 - 30
• 1680 - 20
• 2470 - 300
• 1230 - 200

As you solve these, remember to look for zeros at the end, and see if you can drop them. You can also try breaking numbers apart like 800 + 60 or 1,400 as 1,000 + 400 if that feels more comfortable.