Year 5

Using derived facts to multiply mentally

Year 5

Using derived facts to multiply mentally

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Lesson details

Key learning points

  1. In this lesson, we will use our knowledge of multiplying and dividing by 10, 100 and 1000 to derive facts from known facts. We will then use the distributive law and derived facts to multiply by choosing the most efficient and effective representations.

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5 Questions

Q1.
The strategy of separating a number into its individual units of value is commonly known as?
Approximation
Guessing
Correct answer: Partitioning
Rounding
Q2.
Half of 24 is also the same as:
240 ÷10
Correct answer: 48 ÷ 4
72 ÷ 3
96 ÷ 2
Q3.
The bar model below is used to help divide or multiply numbers. What number should be placed in the top white boxes?
An image in a quiz
12
Correct answer: 15
40
6
Q4.
Which of the following number sentences will help you to solve the calculation 25 x 8?
100 x 4
250 x 80
Correct answer: 50 x 4
50 x 8
Q5.
Which derived fact helps me to mentally solve 240 ÷ 5?
120 ÷ 10
120 x 10
48 ÷ 10
Correct answer: 48 x 10

5 Questions

Q1.
Which of the following methods for answering a multiplication questions is NOT a mental strategy?
Array models
Blank number line
Marked number line
Correct answer: Short multiplication
Q2.
Today we discussed distributive law in relation to multiplication. But which of the following number sentences does NOT correctly represent distributive law?
13 x 24 = 10 x 24 + 3 x 24
19 x 17 = 19 x 10 + 19 x 5 + 19 x 2
Correct answer: 26 x 14 = 20 x 10 + 6 x 4
32 x 7 = 30 x 7 + 2 x 7
Q3.
Which of the following representations would be efficient for the calculation 317 x 23?
Correct answer: Array models
Cuisenaire Rods
Dienes
Q4.
For which of these calculations would you consider using a mental strategy and NOT a written method?
456 x 7
572 x 6
Correct answer: 910 x 12
923 x 6
Q5.
Which calculation do the dienes represent?
An image in a quiz
Correct answer: 13 x 6
16 x 6
603 x 6
63 x 6