Video: KS2-M16 • Paper 3 • Question 13

Lara chooses a number less than 20. She divides it by 2 and then adds 6. She then divides this result by 3. Her answer is 4.5. What was the number she started with?

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Video Transcript

Lara chooses a number less than 20. She divides it by two and then adds six. She then divides this result by three. Her answer is 4.5. What was the number she started with?

To find the missing number, we’ll need to start with the answer and work backwards. Lara’s answer was 4.5. She reached this number by dividing the previous number by three. So if we multiply 4.5 by three, this will tell us what the previous number was.

Four times three is 12. 0.5 times three is 1.5. 12 and 1.5 is 13.5. Lara had added six to this number. To work backwards, we need to subtract six. 13.5 take away six equals 7.5. Lara reached this number by dividing by two. We’re working backwards. So we need to multiply by two. 7.5 multiplied by two is 15. We know that Lara originally chose a number less than 20. 15 is less than 20. The number Lara started with was 15.

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