tính nhẩm a.312×101 b.312×99 c169.101 d169x99

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1. Đáp án:

   $\\$

   `a,`

   `312 × 101`

   `= 312 × (100 + 1)`

   `= 312 × 100 + 312 × 1`

   `= 31200 + 312`

   `= 31512`

   $\\$

   `b,`

   `312 × 99`

   `= 312 × (100 – 1)`

   `= 312 × 100 – 312 × 1`

   `= 31200 – 312`

   `= 30888`

   $\\$

   `c,`

   `169 × 101`

   `= 169 × (100 + 1)`

   `= 169 × 100 + 169 × 1`

   `= 16900 + 169`

   `= 17069`

   $\\$

   `d,`

   `169 × 99`

   `= 169 × (100 – 1)`

   `= 169 × 100 – 169 × 1`

   `= 16900 – 169`

   `= 16731`

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2. `a) 312 . 101`

   `= 312 . ( 100 + 1)`

   `= 312 . 100 + 312 . 1`

   `= 31 200 + 312`

   `= 31512`

   ————————–

   `b) 312 . 99`

   `= 312 . ( 100 – 1)`

   `= 312 . 100 – 312 . 1`

   `= 31200 – 312`

   `=30888`

   ————————–

   `c)169.101`

   `= 169 . ( 100 + 1)`

   `= 169 . 100 + 169 . 1`

   `= 16900 + 169`

   `= 17069`

   ——————————

   `d)169.99`

   `= 169 . ( 100 – 1)`

   `= 169 . 100 – 169 . 1`

   `= 16900 – 169`

   `=16731`

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