Ten More, Ten Less — Mental Math With Two-Digit Numbers

About this activity

A number like 34, 57, 60, or 82 pops up with the words ten more or ten less, and the child works it out in their head and taps the answer from four choices. It's a free, interactive Grade 1 activity that plays right in the browser on a tablet, phone, or classroom computer, with nothing to install and no account.

The key insight is that finding ten more or ten less does not need counting at all — only the tens digit changes while the ones stay exactly the same, so 34 and ten more is 44, and 57 and ten less is 47. The wrong choices are nearby numbers, including ones that change the ones digit, so a child who counts up one by one or just adds a ten in the wrong place will notice it does not fit. The point is to see the tens, not to count.

It is aligned to Common Core 1.NBT.C.5 — mentally finding 10 more or 10 less than a two-digit number, without having to count. No timer, no score — just calm, playful practice.

What's inside this activity

• Designed for Grade 1 learners (ages about 6–7)
• Common Core strand: Number & Operations in Base Ten
• Aligned to Common Core standard 1.NBT.C.5

How to play

Read the number and whether the prompt asks for ten more or ten less.

Work it out in your head — change the tens, keep the ones — then tap the number you think is right.

Take all the time you need; there is no timer and no score, and you can try again.

What your child practices

• Finding 10 more or 10 less than a two-digit number in your head
• Noticing that only the tens digit changes while the ones stay the same
• Reading whether the prompt asks for ten more or ten less
• Building place-value sense for numbers up to 100

Learning goals

Mentally find 10 more and 10 less than any two-digit number — the focus of Common Core 1.NBT.C.5.

Understand that adding or removing a ten changes only the tens digit.

Build the place-value and mental-math foundation for adding and subtracting within 100.