The Sharing Jar — Make It Fair (Find the Missing Number)

About this activity

Pim and Bo scoop moon-beads into their jars at The Sharing Jar, and one jar always ends up fuller — so the child finds the missing number that makes it fair: how many more the quiet jar needs, how big the gap is, or how many there were to start, tapped on tiles from 0 to 10. It's a Grade 1 math activity that runs in the browser with no account.

The numbers stay small, but the unknown moves around — sometimes it is the amount to add, sometimes the difference, sometimes the starting amount that has to be uncovered. That is the whole point: the child is not just adding two numbers, but figuring out which part is missing and how to find it, using counting-on and fact-family thinking. Saying the number out loud before tapping it ties the spoken answer to the written numeral.

It is aligned to Common Core 1.OA.D.8 — finding the unknown number in an addition or subtraction situation, in any position. 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: Operations & Algebraic Thinking
• Aligned to Common Core standard 1.OA.D.8

How to play

Read the two jars and the question — how many more beads does the quiet friend need to be fair?

Work it out, say the kind number, then tap that numeral on the tiles from 0 to 10 and press Check.

Not quite? Try again as many times as you like — there is no timer and no score.

What your child practices

• Find the missing number when the unknown is the part to add, the difference, or the start
• Use counting-on and fact families to make two amounts equal
• Work out how much more one group has than another within 10 and a little beyond
• Connect a spoken number to the written numeral by saying it before tapping

Learning goals

Find the unknown number in an addition or subtraction story — the focus of Common Core 1.OA.D.8.

Understand that the missing part can sit anywhere — the sum, an addend, or the starting amount.

Build the equal-and-fair number sense that early addition and subtraction depend on.