Comet's Big Leaps — 10 & 100 More or Less (Grade 2)

About this activity

Comet the kangaroo lands on a three-digit number — 247, 362, 415, 683 — and makes a leap of 10 more, 10 less, 100 more, or 100 less; the child works it out mentally and types where Comet lands on the keypad. Comet's Big Leaps is a free Grade 2 math activity about adding and subtracting 10 and 100 in your head that plays right in the browser with no sign-up.

The activity is designed to build place-value intuition rather than counting. Adding 10 to 247 changes only the tens digit to give 257; subtracting 100 from 683 changes only the hundreds digit to give 583; the ones stay put either way. Because the child types the answer instead of choosing from cards, there is no guessing — they have to find the one digit that moves and leave the rest alone, which is the heart of mental ten- and hundred-jumps.

It is aligned to Common Core 2.NBT.B.8 — mentally adding 10 or 100 to, and subtracting 10 or 100 from, a number 100 to 900. No timer, no score — just calm, playful practice.

What's inside this activity

• Designed for Grade 2 learners (ages about 7–8)
• Common Core strand: Number & Operations in Base Ten
• Aligned to Common Core standard 2.NBT.B.8

How to play

Read Comet's starting number and the leap — 10 more, 10 less, 100 more, or 100 less.

Work it out in your head and type where Comet lands on the keypad.

Enter your answer and try again if needed — there is no timer and no score.

What your child practices

• Add and subtract 10 to a three-digit number in your head
• Add and subtract 100 to a three-digit number in your head
• Notice that only the tens or hundreds digit changes while the ones stay the same
• Type a calculated answer rather than choosing from given options

Learning goals

Mentally add and subtract 10 and 100 with three-digit numbers — the focus of Common Core 2.NBT.B.8.

Understand which place-value digit changes with each kind of leap.

Build the mental-math fluency that supports larger addition and subtraction.