Addition, subtraction and place value to 100

Se basa en

Requisitos previos obligatorios, hasta el fondo: 2

Aprenderás a

• Add and subtract within 20 fluently, and within 100 using tens and ones.
• Explain that the equals sign means 'has the same value as', so that 7 = 3 + 4 and 3 + 4 = 4 + 3 are both true.
• Represent two-digit numbers as tens and ones and use this to compare them.

Definición

• Addition combines two collections with no members in common; a + b is the number of members of the combined collection.
• Subtraction a − b (with b ≤ a) is the number left when b members are taken from a collection of a members, or the difference between two amounts.
• In a two-digit numeral, the left digit counts tens and the right digit counts ones.

Teorema

• Addition is commutative and associative: a + b = b + a and (a + b) + c = a + (b + c).
• Subtraction undoes addition: (a + b) − b = a.
• Adding zero changes nothing.

Errores frecuentes

• Reading '=' as 'the answer comes next', so that 7 = 3 + 4 seems wrong.
• Thinking subtraction is commutative, for example that 3 − 5 = 5 − 3.
• Reading 52 as 'five and two' rather than five tens and two ones.

Conduce a

Descubrimientos opcionales

• Doing and undoing 'Add 3' and 'take away 3' are actions that undo each other.
• Integers Can we take 5 away from 3? Extending the whole numbers to the integers makes every subtraction possible.

Itinerarios de aprendizaje

• Conventional K–12 progression

Lecturas complementarias

• Hung-Hsi Wu, Understanding Numbers in Elementary School Mathematics (2011)