This short video and interactive assessment activity is designed to teach fourth graders about distance between items.

This short video and interactive assessment activity is designed to teach third graders about multiples - word problems.

This short video and interactive assessment activity is designed to teach third graders about multiplication problems involving grouping of items.

This short video and interactive assessment activity is designed to teach second graders about multiplication sentences from illustrations (numbers 2, 3, 4, 5, and 10).

This Nrich problem provides the children with an opportunity to practice multiplying a multiple of 10 by another multiple of 10. It also reinforces learning about equations being balanced and may lead to conversations about common factors. It encourages children to record their results, notice patterns and make predictions.

This short video and interactive assessment activity is designed to teach fourth graders about place value problems involving items.

This short video and interactive assessment activity is designed to teach fifth graders about multiplying three or more fractions and whole numbers.

This short video and interactive assessment activity is designed to teach fourth graders about multiplying and dividing - missing number.

This short video and interactive assessment activity is designed to teach fourth graders about multiplying and dividing - missing operation.

This Nrich problem is an appealing way for children to recognize, interpret, describe and extend number sequences. Developing their own patterns, as in the later part of the activity, provides an opportunity for them to justify their own thinking, and evaluate others' patterns.

This short video and interactive assessment activity is designed to teach third graders about number riddles (numbers up to 100,000).

This short video and interactive assessment activity is designed to teach third graders about one-step conversions involving multiples of ten.

Challenging math problems worth solving.

The name “Open Middle” might sound like a strange name for a website about math problems. However, it references a very specific type of problem we try to encourage here. Most of the problems on this site have:
* a “closed beginning” meaning that they all start with the same initial problem.
* a “closed end” meaning that they all end with the same answer.
* an “open middle” meaning that there are multiple ways to approach and ultimately solve the problem.

Open middle problems generally require a higher Depth of Knowledge than most problems that assess procedural and conceptual understanding. They support the Common Core State Standards and provide students with opportunities for discussing their thinking.

In this video lesson, students will learn about linear programming (LP) and will solve an LP problem using the graphical method. Its focus is on the famous "Stigler's diet" problem posed by the 1982 Nobel Laureate in economics, George Stigler. Based on his problem, students will formulate their own diet problem and solve it using the graphical method. The prerequisites to this lesson are basic algebra and geometry. The materials needed for the in-class activities include graphing paper and pencil. This lesson can be completed in one class of approximately one hour. If the teacher would like to cover the simplex algorithm by George Dantzig as an alternative solution method, an additional whole class period is suggested.

Understand how to calculate perimeter and find an unknown side if the perimeter is known.

This short video and interactive assessment activity is designed to teach fourth graders about four operations - missing operation.

This short video and interactive assessment activity is designed to teach fourth graders about adding, subtracting, and multiplying with parentheses - missing operation.

This short video and interactive assessment activity is designed to teach third graders about place value problems involving money.

In this Nrich activity, students explore combinations in a situation with constraints. The combinations are complicated by sets and subsets. The situation uses a Venn Diagram.