The purpose of this activity is for students to work with number lines that only have multiples of 5 or 10 labeled and do not start with 0. Students reason about how a number line can be accurate without all the whole numbers labeled. Students use the numbers that are labeled to locate specific numbers on number lines. Students rely on the regular structure of the number line and the counting sequence in order to accurately place numbers (MP7).

• Display the number line labeled 20, 30, 40, 50, 60.
• Invite 1–2 previously identified students to share how they located 48.
• “¿Cómo saben que su punto está a la distancia correcta desde 0?” // “How do you know your point is the right distance from 0?” (It’s like when we measured from different spots on a ruler. The tick marks are spaced the same space apart and count by 1 length unit. We could draw the line back and find where 0 is.)
• “La representación de una recta numérica no puede representar todos los números con marcas, puntos o etiquetas. Podemos usar lo que sabemos basándonos en los números que están marcados para ubicar otros números” // “A number line representation cannot represent all numbers with tick marks, points, or labels. We can use what we know based on the numbers that are labeled to locate other numbers.”

The purpose of this activity is for students to locate numbers up to 100 on a number line. They complete number lines that are labeled with multiples of 5 or 10 by using what they know about length on the number line and counting by 5 and 10. They use the labeled tick marks to locate and represent numbers within 100. When students explain to one another how the located different numbers on the number lines they construct viable arguments  and may critique each other's reasoning (MP3).

• Display the image of an incomplete number line labeled with 10 and 50.
• “¿Cómo podemos encontrar el 35 sin completar los números que faltan?” // “How could you find 35 without filling in the missing labels?” (We could count back from 50. We could count on from 10.)
• Invite previously identified students to explain how they found the labels and used them to locate 35.
• Complete the number line as students explain.