 Complete multiplication statements to make a target number

Lesson

The value of our number

When we make a number with decimals, it's important to think about the value of our digits. We know that 30 means 3 tens, and the 0 means 0 units. But what about 0.3? That is 3 tenths, a number less than one. If we multiply something by a number less than $1$1, our answer is going to be smaller than the number we started with. This is different to multiplying whole numbers to create a new number, where the answer ends up larger.

In the first video, we think about what number we need to multiply $4$4 by, to get $2$2 as our answer.  The answer is smaller, so we need to multiply $4$4 by a number smaller than $1$1.  We also look at how to rule out possible answers, by considering those that cannot be correct, and why!

In the second video, we look at possible answers when we multiply two decimals together when they are both less than 1.  Instead of only solving a number problem mathematically, we look at the value of the digits and thinking about which numbers are bigger.

Remember!

Often, we can rule out incorrect answers, making the job of choosing the correct answer much easier.

Worked Examples

Question 1

Let’s play a game called target number. Here’s how it works: I give you a target number and starting number and you tell me what I need to get there.

For example, our target number is $0.4$0.4, and if I tell you the number $0.2$0.2 you would say $2$2, because $0.2\times2=0.4$0.2×2=0.4.

Find the missing number below if $0.3$0.3 is our target number.

1. $0.1\times\editable{}=0.3$0.1×=0.3

Question 2

Which of the options below make $6.8$6.8? There might be more than one right answer, so select all the correct options.

1. $2\times3.4$2×3.4

A

$5\times1.5$5×1.5

B

$6\times0.8$6×0.8

C

$6.8\times1$6.8×1

D

$2\times3.4$2×3.4

A

$5\times1.5$5×1.5

B

$6\times0.8$6×0.8

C

$6.8\times1$6.8×1

D

Question 3

Let’s play a game called target number. Here’s how it works: I give you a target number and starting number and you tell me what I need to get there.

For example, our target number is $0.616$0.616, and if I tell you the number $4$4 you would say $0.154$0.154, because $0.154\times4=0.616$0.154×4=0.616.

Find the missing number below if $0.954$0.954 is our target number.

1. $\editable{}\times3=0.954$×3=0.954

Outcomes

NA5-3

Understand operations on fractions, decimals, percentages, and integers