## Counting & Cardinality

**Problem 537:A Solar Storm Number Puzzle**

Students solve 10 problems using positive and negative numbers, addition, subtraction and multiplication
to find the missing words in a short essay about solar storms.
[Grade:3-5 | Topics: integer arithmetic; positive and negative numbers]
(PDF)

**Problem 543:Timeline for Planet Formation**

Students calculate time intervals in millions and billions of years from a timeline of events
[Grade: 3-5 | Topics: time calculations; integers]
(PDF)

**Problem 269: Parts Per Hundred (pph) ** Students work with a common unit to describe the number of objects in a population. Other related quantities are the part-per-thousand, part-per-million and part-per-billion.
[Grade: 3-5 | Topics: counting, unit conversion]

**Problem 173: Groups, Clusters and Individuals ** Students determine the number of individual objects given the number of groups and the number of individuals in an average group for clusters of stars and galaxies.
[Grade: 3-5 | Topics: multiplication]

**Problem 356: Calculating Molecular Mass**

Students count hydrogen, carbon and oxygen atoms in a molecule of adefovir dipivoxil and calculate its mass and formula.[Grade: 6-8 | Topics: Counting; Scientific Notation]
(PDF)

**Problem 294: Star Cluster Math** A simple counting exercise involving star classes lets students work with percentages and ratios.
[Grade: 4-6 | Topics: Counting; percentage; scaling]

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

**Problem 123 ****A Trillion Here...A Trillion There **
Students learn to work with large numbers, which are the heart and soul of
astronomical dimensions of size and scale. This activity explores the number 'one trillion' using examples drawn from
the economics of the United States and the World. Surprisingly, there are not many astronomical numbers commonly in use that are as big as a trillion.
[Grade: 5-9 | Topics:add, subtract, multiply, divide.]