Page 89 - More! 1_Student_s book

e a Read the texts about shortcuts.

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Maths shortcuts ......... *", ..,II?
look at the Iaat digit.
Is it 5 or O'? - The number is
divisible by 5.

, •• number divi.ib'. by 4?
Look at the last 2 digits.
• Are they DO'? ..... The number is
divisible by 4.
4598376599997800 Yes!
• Is the last two-digit number
I. a number divisible by 9?
divisible by 4?
Add up the digits. Divide the sum by 9. Is it possible? 3564785476899938 Yes!
Yes? ..... The number is divisible by 9. 3EH·4=9
No? ..... The number is not divisible by 9. Yes"'" The whole number is
divisible by 4 .
Dividing or multiplying by 5 i •••• y!
Remember that 5 is half of ten. MulClplying by 11 .. any!
To multiply 5 x 86. work out 10 x 86 first: 860. Remember that 11 . 10 + 1.
Then divide in half: 430 To multiply 49 x 11.
To divide 98 by 5. divida by ten first: 9.8 multiply 49 x 10 first: 490.
Then double the answer: 19.6 Than add 49: 490 + 49 .. 539

b Can you think of more shortcuts? Tell your class.

Mini-project

o Work with a partner.

a Tick the answers to these questions. Do not use a calculator.
Is 23 divisible by 3? DYes D No
2 Is 2905 divisible by 5? DYes D No
3 Is 34987465 divisible by 9? DYes D No
4 Is 75938627824 divisible by 4? DYes D No
5 Is 9427211163291 divisible by 3? DYes D No
6 Is 45879435768903212873 divisible by 9? DYes D No

b Find the answers to these questions quickly.
H ow much is 73 x 1P 3 How much is 128 divided by 5?
2 How much is 5 x 99?

o With your partner, write a quiz for another pair of students.

UNIT 7