THE MOST IMPORTANT CONCEPT

Unit 9 : More addition and subtraction ​

Estimate : rounding to nearest tens

estimate 111 = 110

estimate 346 ​= 350

if the ones digit less than 5 you will rounding down

like : estimate 234 = 230 ​

addition with no regrouping : there's no carrying of tens or hundred

like : 231 + 145 = 376

The answer can simply be written below each place value column . ​

More addition and subtraction ​

the sum of the tens place is more than 9 ( 2 digits ) ​

162 + 262 = 424​

addition with regrouping tens ​

The sum of the ones place is more than 9 ( 2 digits )

126 + 226 = 352 ​

Addition with regrouping ones ​

addition with regrouping ones ​and tens

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I can't subtract The Tens place except by borrowing

Like : 658 - 293 = 365​

Subtraction with regrouping tens ​

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I can't subtract The Ones place except by borrowing​

Like: 233 - 117 = ​116

Subtraction with regrouping ones ​

Subtraction with regrouping Ones and Tens ​

most important concepts ​

Using Trial and improvement : A method to finding the answer by try ​

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Exchange : Replacing ​( borrowing )

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the most important concepts . ​