# 2.OA.2. Fluently add and subtract within 20 using mental strategies. By end of Grade 2, know from memory all sums of two one-digit numbers

A fun game to practise mental addition skills. The game was designed to cover all the mental addition objectives in the new math curriculum. You can choose one objective, or choose all the objectives for a year group.

This game, together with all the other crystal crash games, is available as a single iPad or Android app.

Bubble Pop - Number Bonds

A great way to practise number bonds and mental addition. Levels include: number bonds to 10, 20, 50 and 100 as well as addition pairs with a total of up to 20, 50 or 100. Look at the target at the top of the screen and then aim your bubble to make that target.

As a teacher I know how important it is that children know their number bonds (pairs of numbers that add up to 10, 20, 50 or 100), and can add quickly mentally. Repetition is essential in learning number bonds. This game is designed to make the process fun.

Children have to aim their bubble to make a given sum. As they progress the levels get harder; they have less time, or less bubbles to shoot. Each correct answer is accompanied by an image to reinforce the number bond they have found.

This game is available on iPad, iPod and iPhone, as well as on android phones and tablets.

Shoot the spaceship with the correct answer and dodge the incoming fire. A fun game to practise a wide range of key mathematical skills.

There are over a hundred carefully differentiated levels linked to objectives from the new maths curriculum. The game can be used to teach: Multiplication, Addition, Reading Numbers, Subtraction, Fractions of Numbers, Roman Numerals, Rounding Numbers, Division, Converting Fractions to Decimals, Converting Fractions to Percentages, Telling the Time in Words, Recognising Multiples, Factors, Prime, Square and Cube Numbers, and Simplifying Fractions. A full list of levels is below. This game is also available as an iOS and Android app.

Subtraction - Crystal Crash

The game was designed to cover all the mental subtraction objectives in the new math curriculum. You can choose one objective, or choose all the objectives for a year group.

This game, together with all the other crystal crash games, is available as a single iPad or Android app.

 1) Subtract numbers from up to 10 (Y1) 6) Subtract from 100 (multiples of 10) (Y3) 11) Subtract tens from a three-digit number (Y3) 16) Subtract combinations of decimals (1dp) (Y4) 2) Subtract numbers from up to 20 (Y1) 7)Subtract from 100 (multiples of 5) (Y3) 12) Subtract hundreds from a three-digit number (Y3) 17) Subtract a decimal (2dp) from 1  (Y5 & Y6) 3) Subtract ones from a two-digit number (Y2) 8) Subtract from 100 (Y3 & Y4) 13) Subtract a decimal (1dp) from 1 (Y4 & Y5) 18) Subtract combinations of three-digit numbers (Y5 & Y6) 4) Subtract tens from a two-digit number (Y2) 9) Subtract from 1000 (multiples of 100) (Y3 & Y4) 14) Subtract a decimal (1dp) from 10 (Y4 & Y5) 19) Subtract combinations of decimals (2dp) (Y5 & Y6) 5) Subtract a two-digit number from a two-digit number (Y2) 10) Subtract ones from a three-digit number(Y3) 15) Subtract two-digit numbers from three-digit numbers (y4)

Answer addition and subtraction questions to arrange the dominoes in the correct order as quickly as possible. Lots of choice over level including; add and/or subtract within 20, 50, 100, using decimals or with negative numbers.

A great way to practice number bonds / complementary numbers. Play against the clock and see who can complete the sums quickest. Choose number pairs that equal 10, 20, 50 or 100, or decimals pairs that equal 1.

Add and Subtract on a Number Line

Add and subtract near multiples on a number line. Develop mental methods of addition and subtraction by adding and subtracting a multiple of 10 or 100, and then adjusting. For example add 29 by adding 30 and then subtracting 1.

Balancing Sums

An excellent tool for reinforcing an understanding of the role of the equals sign. Choose one objective, or many. You can choose all the objectives for a single year group (or multiple year groups). You can also choose to balance between different types of calculations (eg addition and multiplication).

Difference using a marked number line

Count on from the smaller number to the larger. As numbers are added to the balance scale they are also shown on the number line. Children should be encouraged to use their knowledge of number bonds to develop efficient mental methods.

Levels include counting up to 10, 20, 50 or 100, finding the difference between 2-digit numbers and decimals.

ITP Difference

I have created my own version of this ITP which allows you to find the difference between two 2-digit numbers and shows this on a number line.

View full screen in your browser.  This ITP allows you to compare two rows of beads and to analyse the calculations they can represent. It can be used to promote the language of addition and subtraction, particularly the interpretation of difference. The ITP operates as a series of animations which show how the rows of beads can be represented by two number lines and then as a single number line with the difference indicated by a ‘jump’.

This resource is freely available to download from the archived Primary Framework site.

ITP Number Facts

View full screen in your browser.  This ITP displays up to 20 coloured counters and the corresponding addition sentence. The number of counters you select, appear on the screen in purple. Click on any counter to change its colour, the number sentence also changes. To hide and reveal the number sentence, click on the box with the question marks. You can replace a number in the number sentence with a question mark by clicking on the number, and drag counters around the screen to form groups. Addition can be changed to subtraction by clicking on the addition sign in the box. Counters can be dragged into the displayed box, which you can make opaque to hide the counters.
The ITP can be used to model addition by combining and counting, and subtraction by partitioning and taking away. The hide and reveal options allow you to pose questions with unknown numbers in different positions in the number sentence. Partitioning counters in different ways helps children to identify all sums and differences of numbers to 20.

This resource is freely available to download from the archived Primary Framework site.

Number Facts Beat The Clock

Score as many points as you can before the time runs out. A number of levels including addition, subtraction, multiplication, division and matching fractions and decimals.

*Updated 30th May 2013 - choose multiple objectives, or objectives grouped by national curriculum level. The game also now includes a scoreboard. An iPad version is also available.

Number Bonds

October 2012: New game added in which number bonds are represented visually using base-ten blocks and a number line.

Find pairs of numbers with a given total. Play against the clock.

Ordering Calculations

Order the calulations from those with the least value to the greatest. Lots of levels, including; addition pairs to 20, addition pairs to 100, addition and subtraction of multiples of 10, and multiplication of numbers up to 10.