Year 4 (Grade 4)

2, 4, 6, 8 — pick a step and watch a marker hop along.

1, 2, 3 — tap to count, hear the rhythm, watch the blocks stack up.

1 to 100 in a 10×10 grid. Click cells to colour them and spot patterns.

What's the difference between a number, a numeral, and a digit?

Break 47 into 4 tens + 7 ones — and put it back together.

Why 305 isn't the same as 350 — see digits move between columns.

Drag a marker and see negatives, fractions and decimals come alive.

Three (3), third (3rd), bus #3 — same digits, different jobs.

I, V, X, L, C, D, M — type a year and watch it become a Roman numeral.

Count two stacks of blocks together — see how + works as combining.

Take some away. Watch the blocks vanish and what's left appear.

3 × 4 is a rectangle of dots. Drag the sides and watch the total.

Two-digit × two-digit, step by step on a grid.

1× to 12× in a clean grid. Hover any cell to see the row × column highlight.

GCD, LCM and divisibility rules — the hidden structure of numbers.

Divide, multiply, subtract, bring down — the four-step dance, animated.

Share 12 cookies between 3 friends — see division as fair sharing.

Quick tricks to check whether a number is divisible by 2, 3, 4, 5, 6, 9 or 10.

Why your calculator throws an error and what undefined really means.

Decimals with no pattern, no repeat, no end — like √2 and π.

Negative + positive, and how to think about each.

Find primes with the Sieve of Eratosthenes — interactive.

GCD, LCM and divisibility rules — the hidden structure of numbers.

5! = 5×4×3×2×1 = 120. Click and watch the tree fan out.

Every number on the number line — the big family.

Distance from zero, ignoring sign — |−7| = 7.

6.02 × 10²³ — a tidy way to write very big or very small numbers.

Round to the nearest 10, 100, or decimal place — and the tie-breaker rules.

Two numbers whose only common factor is 1 — they share no factors.

Counting → naturals → integers → rationals → reals → complex. The story.

Why 305 isn't the same as 350 — see digits move between columns.

Tenths, hundredths, thousandths — and why they line up.

Base 16 — A through F take over after 9. Drives all those CSS colours.

1/3 = 0.333…, 1/7 = 0.142857142857… every fraction has a pattern.

Three ways to write the same part of a whole — and how to switch between them.

PEMDAS — brackets first, then powers, then × and ÷, then + and −.

Slice a circle, compare halves and thirds, add fractions visually.

Two cups flour to one cup sugar — scale the recipe and watch the ratio hold.

1 : 1.618 — the rectangle that nests inside itself forever.

Decimals with no pattern, no repeat, no end — like √2 and π.

Three ways to write the same part of a whole — and how to switch between them.

What you can measure: length, mass, capacity, time, temperature.

A standard chunk you compare other things against — and why standards matter.

Convert any length, mass, volume, area, speed, or temperature — with the cancel-the-units trick.

Inch, foot, pound, gallon, acre, Fahrenheit — the system that runs the US, with a visual size chart.

kilo, mega, giga, milli, micro, nano — 14 prefixes that scale every metric unit.

mm, cm, m, km — and inches and feet.

mm, cm, m, km — base 10, easy to convert.

Inch, foot, yard, mile — and the conversions you really need.

Read clocks, count minutes, work with durations.

How many days in this month? When does the leap year fall?

Twelve months, names and origins — and how many days each one has.

Seven days, where the names come from, and how the modern week was set.

Sunrise to sunrise — and the 24 hours in between.

One trip around the sun — and why it's not exactly 365 days.

Spring, summer, autumn, winter — and the tilt of the Earth that drives them.

Seconds, minutes, hours, days — convert between any two.

Measuring elapsed time — for races, recipes and physics experiments.

Two ways to display the same time — read either at a glance.

How many days in this month? When does the leap year fall?

Why every fourth year — except some — gets an extra day.

Read clocks, count minutes, work with durations.

Twelve months, names and origins — and how many days each one has.

Seven days, where the names come from, and how the modern week was set.

Sunrise to sunrise — and the 24 hours in between.

One trip around the sun — and why it's not exactly 365 days.

Spring, summer, autumn, winter — and the tilt of the Earth that drives them.

Seconds, minutes, hours, days — convert between any two.

Measuring elapsed time — for races, recipes and physics experiments.

Two ways to display the same time — read either at a glance.

Same shape, different size — corresponding sides scale together.

Same shape AND same size — SSS, SAS, ASA, AAS, RHS prove it.

The three angles always sum to 180°. Drag to convince yourself.

Centroid, circumcenter, incenter, orthocenter — four points every triangle hides.

Resize a rectangle and see area and perimeter follow.

Triangle 180°, quad 360°, pentagon 540° — sum grows by 180° per side.

Walk around a polygon — the turns always add to 360°.

Two sides always add to more than the third — or no triangle.

One 90° corner — and the home of Pythagoras and trig.

Three equal sides, three 60° angles — the most symmetric triangle.

Two equal sides — and the base angles are equal too.

All sides different — no symmetry.

The simplest right triangle in whole numbers — used since ancient Egypt.

Four right angles, opposite sides equal — the most familiar shape.

Three sides, two sides and an angle — build a triangle from any combination.

Spin a shape — does it look the same before a full turn?

Circle, triangle, square, polygon — names, sides, properties.

Three sides, four, five, six… and the angle each interior corner gets.

Cubes, spheres, cylinders — drag a dimension and watch volume grow.

(4/3)πr³ and 4πr² — Archimedes worked these out without calculus.

What's a cube in 4 dimensions? Or 5? You can almost picture it.

Polyhedra, prisms, pyramids, Platonic solids — Euler's V−E+F = 2.

Six squares, twelve edges, eight corners — the simplest 3D solid.

Every point the same distance from the center — the most efficient surface.

Two circles joined by a tube. Cans, pipes, drums.

A circle pulled to a point. Ice-cream, party hats, traffic markers.

A donut. One hole, but a surprising amount of geometry.

Same shape, top and bottom — connected by rectangles.

A polygon base, all sides meeting at one peak.

There are exactly five — tetrahedron, cube, octahedron, dodecahedron, icosahedron.

Unfold a solid into a flat net — a paper template you can cut and rebuild.

Four triangular faces — the simplest 3D solid.

Eight triangular faces — like two pyramids glued base to base.

Twelve pentagonal faces — one of the five Platonic solids.

Twenty triangular faces — the most spherical of the Platonic solids.

What comes next? Numbers, colors, shapes — the first step into algebra.

1, 4, 9, 16… spot the pattern, predict the next.

≠, ≈, ∝, ∞ — every symbol an algebra student needs.

Slices of a circle — each one a percentage of the whole.

Bar, pie, line — the same numbers told three ways.

Compare categories at a glance — taller bar means bigger.

Connect points to track change over time.

Pictures stand in for counts — friendly charts for small data.

Bar charts for grouped numerical data — bins on the x-axis.

One dot per data point — see exactly where each value lands.

The fastest way to count by hand — strokes in groups of five.

How often each value (or range) appears — turn a list into a table.

Running total — and the curve it builds.

Two variables, one dot per data point — patterns appear.

An old-school way to see distribution without losing the actual numbers.

Design good questions, gather honest answers, analyse the results.

Mean, median, mode, range — interactive.

Add them all, divide by how many — the everyday average.

Some data points count more — multiply, then divide by total weight.

On average, how far is each value from the mean?

The middle value when sorted — robust against outliers.

Add up coins and bills.

Cents are decimals of a dollar — every transaction is decimal arithmetic.

Build $1.37 with the fewest coins — a classic problem.

Hourly, salaried, overtime — and how to compare offers fairly.

20% off — what does that actually cost?

What interest is, why borrowers pay it, why savers earn it.

Interest on the original amount only — clean and predictable.

Interest earns interest. Slide the years and watch the curve bend up.

Why A = P(1 + r/n)^(nt) — and where every letter comes from.

Income in, expenses out — build a balanced month.

Convert between dollars, euros, pounds and more.

What a return is, what risk is, and why time helps.

Regular payments — how to value a stream of cash flows.

What a future dollar is worth today — discount it back.

Sum of discounted cash flows — positive means it's worth doing.

The discount rate that makes NPV zero — investing's headline number.

Pool small premiums, pay big claims — risk-sharing as maths.

When does owning beat renting? A comparison you can run with numbers.