## Number and Operations - Fractions

**Problem 546: The Relative Sizes of Planets and other Objects**

Students use proportional information to determine the relative scales of planets and large moons across the solar system.
[Grade: 3-5 | Topics:scale; proportion]
(PDF)

**Problem 493: Fun with Gears and Fractions **

Students learn about how simple fractions are used to describe gears and gear trains that reduce or increase speed.
[Grade: 4-7 | Topics: multiplying simple fractions]
(PDF)

**Problem 465: Comparing Planets Orbiting other Stars **

Students use simple fraction arithmetic to determine the relative sizes of several new planets recently discovered by the Kepler mission,
and compare these sizes to that of Jupiter and Earth.
[Grade: 3-5 | Topics: scale models; proportions; fractions]
(PDF)

**Problem 464: Big Moons and Small Planets **

Students work with a scaled drawing of 26 large moons in the solar system, and together with an exercise in using simple
fractions, explore the relative sizes of the moons compared to Earth.
[Grade: 3-5 | Topics: scale models; proportions; fractions]
(PDF)

**Problem 297: Atoms - How Sweet They Are!** A simple counting activity is based on atoms in a sugar molecule. Students
calculate ratios and percentages
of various atomic types in the molecule.
[Grade: 4-8 | Topics: Counting; Ratios; percentage]

**Problem 242: Counting Atoms in Molecules ** Students count the number of atoms in a simple molecule and work out some basic fractions, percentages and masses. they also complete
the chemical formula for the compound.
[Grade: 3-6 | Topics: integers; counting similar things; fractions; percentages ]

**Problem 230: Galaxy Distances and Mixed Fractions-** Students use the relative distances to nearby galaxies expressed in mixed numbers to determine distances between selected galaxies.
[Grade: 3-5 | Topics: Basic fraction math.]

**Problem 229: Atomic Numbers and Multiplying Fractions-** Students use a piece of the Periodic Table of the Elements to figure out the identities of atoms based on numerical clues expressed as mixed numbers.
[Grade: 3-5 | Topics: Basic fraction math; mixed numbers.]

**Problem 217: Fractions and Chemistry-** Students study simple chemical equations by using simple proportions and mixed numbers.
[Grade: 3-6 | Topics: Basic fraction math; ratios.]

**Problem 216: Atomic Fractions-** Students study the energy ladders of an atom and work out, using differences between mixed numbers, the energy gained
or lost by an electron as it moves up and down the ladder.
[Grade: 3-6 | Topics: Basic fraction math]

**Problem 215: More Atomic Fractions-** Students study the energy ladders of an atom and work out, using differences between mixed numbers, the energy gained
or lost by an electron as it moves up and down the ladder.
[Grade: 3-6 | Topics: Basic fraction math.]

**Problem 214: Atomic Fractions III-** Students study the energy ladders of an atom and work out, using differences between mixed numbers, the energy gained
or lost by an electron as it moves up and down the ladder.
[Grade: 3-6 | Topics: Basic fraction math.]

**Problem 180: Planets, Fractions and Scales-** Students work with relative planet comparisons to determine the actual sizes of the planets given the diameter of Earth.
[Grade: 4-6| Topics: scale models; decimals; fractions]

**Problem 165: Fractions in Space -** Students explore the many ways that simple fractions come up in the study of planetary motion.
[Grade: 3-5 | Topics: working with fractions; time calculations]