Tens Takeaway! Subtracting Groups of 10 from Big Numbers!

Hi Maths Detectives! Today, we’re practicing a super useful mental maths skill: subtracting multiples of 10 (like 20, 30, or 40) from bigger 3-digit numbers. The great news is, for these problems, the hundreds digit will stay just where it is – we’re not crossing the hundreds boundary! Let’s try a sum like 672 take away 30.

How to Subtract Multiples of 10 (e.g., 672 − 30)

When we subtract a multiple of 10 (like 20, 30, 40, etc.) without crossing the hundreds boundary, we mostly focus on changing the tens digit in our 3-digit number. The hundreds digit and the ones digit often stay the same!

Let’s look at 672 − 30:

• Our starting number is 672. This is made of 6 hundreds, 7 tens, and 2 ones.
• We want to subtract 30, which is the same as 3 tens.
• So, we need to take 3 tens away from the 7 tens we have in 672.
  • 7 tens − 3 tens = 4 tens.
• The hundreds digit (6 hundreds) didn’t change!
• The ones digit (2 ones) also didn’t change in this example!
• So, if we put it all back together: 6 hundreds, 4 tens, and 2 ones makes 642.
• That means 672 − 30 = 642. You’ve successfully taken away those tens!

For all the problems on this page, the hundreds digit won’t need to change.

Your Mission: 18 “Subtract the Tens” Challenges!

Ready to put your skills to the test? Below are 18 mental maths questions. In each one, you’ll subtract a multiple of 10 from a 3-digit number, and the hundreds digit will stay put. Concentrate on that tens place!

(Your web app with the 18 questions will go here.)

Why is Subtracting Multiples of 10 a Super Skill?

• Builds Strong Number Sense: You get really good at understanding how hundreds, tens, and ones work together.
• Foundation for Harder Subtraction: Mastering this helps you get ready for trickier problems.
• Quick Mental Calculations: You’ll become faster at working out these types of sums in your head.
• Useful in Daily Life: Handy for things like working out how much money you have left after spending a bit, or if you’re counting down in tens.

Tips for Parents & Teachers

This activity is designed to help children practise the mental subtraction of a multiple of 10 (e.g., 20, 30, 50) from a 3-digit number, where the operation does not require regrouping from the hundreds place (e.g., 672 − 30 = 642; 481 − 50 = 431).

• Highlight Place Value: Emphasise that it’s the tens digit that changes. The hundreds and ones digits often remain the same in these examples.
• Count Back in Tens: Encourage children to “count back” from the 3-digit number in steps of 10. For 672 − 30, they might think “672… 662, 652, 642.”
• Use a Number Line or Hundred Square: Visually hopping back in groups of ten can be a helpful initial strategy for some children.
• Connect to Known Facts: Relate 7 tens − 3 tens to the simpler fact 7 − 3.