# Mastery: Reasoning and Problem-Solving

Y5

• Draw an acute angle, estimate its size. Write your estimate. Then measure it. How close were you?
Repeat this for an obtuse angle.
• Draw a pentagon with two right angles and two obtuse angles. Can you draw a pentagon with three acute angles?
• True or False?
A quadrilateral could have two reflex angles.
• Draw a straight line divided into three acute angles. Measure two of the angles and calculate the third. Then measure it to check.
• Draw four angles around one point, where one of them measures 90°. Measure and label the other three angles.
• The three angles inside a regular (equilateral) triangle are all 60°, so add to 180°. The four angles inside a regular quadrilateral (square) are all 90°, so add to 360°.
• The sum of the five angles inside a regular pentagon follows a pattern begun by the triangle and square. Can you calculate how big each one is?

Y6
This unit has no separate problem-solving activities for Y6.

In-depth investigation:
Y5
Use Day 1’s investigative Group Activity
Y6 Use the Day 1-2 investigative Group Activity