Unit 9, Lesson 4
Otra mirada al algoritmo estándar
Grado 4
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This Number Talk encourages students to think about the base-ten structure of whole numbers and the properties of operations to mentally solve subtraction problems. The reasoning elicited here will be helpful later in the lesson when students find differences of multi-digit numbers.
Encuentra mentalmente el valor de cada diferencia.
None
Previously, students used the standard algorithm for subtraction to find the differences involving minuends with multiple zeros. They also used the standard algorithm of addition to find an unknown addend that gives a sum with multiple zeros for its digits. In this activity, students make connections between these two ways of reasoning about differences. They also analyze another way to find differences between multi-digit numbers.
Select students to share their calculations, or display:
Kiran
Priya y Han intentan encontrar el valor de
Kiran usa otro método. Explica cómo encuentra Kiran el valor de
“Hoy usamos distintas formas de restarle un número que tiene dígitos que no son cero a un número que tiene ceros” // “Today we used different ways to subtract a number with non-zero digits from a number with zeros.”
“¿Qué estrategia usaron para encontrar la diferencia entre 50,400 y 1,389?” // “What strategy did you use to find the difference between 50,400 and 1,389?” (Display the strategies used in the last question. Or display the three ways here and any additional methods. Ask students to explain each method.)
Using Kiran’s method:
Using Han’s method:
Using Priya’s method
(standard algorithm):
“¿Cuándo puede ser conveniente usar el algoritmo estándar para restar dos números de varios dígitos?” // “When might it be convenient to use the standard algorithm to subtract two multi-digit numbers?” (When most digits in the second number are less than those in the same place in the first number.)
“¿Cuándo podría no ser conveniente usar el algoritmo estándar para restar?” // “When might it be inconvenient to use the standard algorithm to subtract?” (When most digits in the second number are greater than those in the same place in the first number, making it necessary to do multiple rounds of regrouping.)
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En cada caso, encuentra el valor de la diferencia.
En cada caso, encuentra el número que hace que la expresión sea verdadera.