Maths 3 - Lesson 9.1 - CIE 3.1

put hundreds, tens and ones together in different ways to support calculating.

• Regroup

• Exchange

• Compose

• Decompose

Split number into tens and ones or hundreds and ones.

• Regroup

• Exchange

• Compose

• Decompose

roughly calculate or judge the value, number or quantity.

• Regroup

• Estimate

• Compose

• Decompose

Estimate these 2-digit numbers.

84 + 62 = 80 + 60 = 140

--> 84 + 62 = 146

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Estimate these 2-digit numbers.

46 + 75 = 50 + 80 = 130

--> 46 + 75 = 121

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Estimate these 3-digit numbers. (Rounding the number to the nearest 10)

237 + 165 = 240 + 170 = 410

--> 237 + 165 = 402

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Answer explanation

It's true because

Rounding to the nearest 10

237 --> 240

165 --> 170

Estimate these 3-digit numbers. (Rounding the number to the nearest 10)

451 + 287 = 500 + 300 = 800

--> 451 + 287 = 738

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Answer explanation

It's false because

Rounding to the nearest 10

451 --> 450

287 --> 290

Estimate these 3-digit numbers. (Rounding the number to the nearest 10)

342 + 155 = 340 + 160 = 500

--> 342 + 155 = 497

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Estimate these 3-digit numbers. (Rounding the number to the nearest 10)

421 + 137 = 400 + 100 = 500

--> 421 + 137 = 558

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Answer explanation

It's false because

Rounding the number to the nearest 10

421 --> 420

137 --> 140

Estimate these 2-digit numbers.

23 + 58 = 20 + 50 = 70

--> 23 + 58 = 81

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Answer explanation

It's false because

58 round to the nearest 10 is 60

23 + 58 = 20 + 60 = 80