Toán Lớp 5: bài 1 : a, 45 x 113 + 45 x 113 + 113 b,54 x 47 – 47 x 53 – 20 – 27 c, ( 145 x 99 + 145 ) – ( 143 x 101 – 143)

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1. a) 45 xx 113 + 45 xx 113 + 113

   = 113 xx ( 45 + 45+ 1)

   = 113 xx 91

   = 10283

   ———————————–

   b) 54 xx 47 – 47 xx 53 – 20 – 27

   = 54 xx 47 – 47 xx 53 – ( 20 + 27)

   = 54 xx 47 – 47 xx 53 – 47

   = 47 xx ( 54 – 53 – 1)

   = 46 xx 0

   = 0

   —————————————-

   c) ( 145 xx 99 + 145) – (143 xx 101 – 143)

   = ( 145 xx 99 + 145 xx 1) – ( 143 xx 101 – 143 xx 1)

   = [145 xx ( 99 + 1) ] – [143xx ( 101 – 1)]

   = [ 145 xx 100] – [ 143 xx 100]

   = 14500 – 14300

   = 200

   Trả lời
2. a,

   45 × 113 + 45 × 113 + 113

   = (45 + 45 + 1) × 113

   = 91 × 113

   = 10283

   b,

   54 × 47 – 47 × 53 – 20 – 27

   = 54 × 47 – 47 × 53 – (20 + 27)

   = 54 × 47 – 47 × 53 – 47

   = (54 – 53 – 1) × 47

   = 0 × 47

   = 0

   c,

   (145 × 99 + 145) – (143 × 101 – 143)

   = [145 × (99 + 1)] – [143 × (101 – 1)]

   = 145 × 100 – 143 × 100

   = (145 – 143) × 100

   = 2 × 100

   = 200

   Trả lời