19
Problem solving
Textbook: Part 1, lesson 19, pp. 58–60
GoalSolve problems using divisibility rules and diagrams.
New words
problem · masaladiagram · sxemaexpression · ifodachecking · tekshirish
Explanation
To solve a problem we read the condition, make a short note or diagram, plan, calculate and check the answer. Divisibility rules let us know the answer in advance without dividing: asked whether 156 pupils can be split into 4 groups, we test the last two digits 56 – and yes, it can.
Worked examples
The largest three-digit number from the digits 3, 5, 0 divisible by 5 is 530.
156 pupils: 4 groups are possible (56 : 4 = 14), with 39 in each; 5 groups are not (the last digit is 6).
Class activity
“Which teams?”: children use the rules to decide whether a class of 24, 25 or 27 can be split into teams with no one left over.
Practice
1
Write the largest even three-digit number made from the digits 2, 7, 4 (each used once).
742
2
Solve 480 : x = 12.
40
3
A class has 15 girls and 3 more boys than girls. How many pupils are in the class?
33
4
Which of 1 026 and 1 027 is divisible by 9?
1 026