Bài 1: Tính nhanh:
5+ 5 + 5 + 5+ 5 + 5 +5+ 5 + 5 +5
25 + 25 + 25 + 25 + 25 + 25 +25 + 25
45 + 45 + 45 + 45 + 15 + 15 + 15 + 15
2 + 4 + 6 + 8 + 10 + 12 + 14 + 16 + 18
125 + 125 + 125 + 125 – 25 – 25 – 25 – 25
Bài 1: Tính nhanh: 5+ 5 + 5 + 5+ 5 + 5 +5+ 5 + 5 +5 25 + 25 + 25 + 25 + 25 + 25 +25 + 25 45 + 45 + 45 + 45 + 15 + 15 + 15 + 15 2 + 4 + 6 + 8 + 10 + 12
By Natalia
$5+5+5+5+5+5+5+5+5+5$
$=5×10$
$=50$
$25+25+25+25+25+25+25+25$
$=25×8$
$=200$
$45+45+45+45+15+15+15+15$
$=45×4+15×4$
$=180+60$
$=240$
$2+4+6+8+10+12+14+16+18$
$=(2+18)+(4+16)+(6+14)+(8+12)+10$
$=20+20+20+20+10$
$=90$
$125+125+125+125-25-25-25-25$
$=(125-25)+(125-25)+(125-25)+(125-25)$
$=100+100+100+100$
$=400$
Đáp án:
5+ 5 + 5 + 5+ 5 + 5 +5+ 5 + 5 +5
= 5 × 10
= 50
25 + 25 + 25 + 25 + 25 + 25 +25 + 25
= (25 + 25) + (25 + 25) + (25 + 25) +(25 + 25)
= 50 + 50 + 50 + 50
= 50 × 4
= 200
45 + 45 + 45 + 45 + 15 + 15 + 15 + 15
= (45+15) + (45+15) + (45+15) + (45+15)
= 60 + 60 + 60 + 60
= 60 × 4
= 240
2 + 4 + 6 + 8 + 10 + 12 + 14 + 16 + 18
= (2+18) + (4+16) + (6+14) + (8+12) + 10
= 20 + 20 + 20 + 20 +10
= 20 × 4 +10
= 80 + 10
= 90
125 + 125 + 125 + 125 – 25 – 25 – 25 – 25
= (125-25) + (125-25) + (125-25) + (125-25)
= 100+100+100+100
= 100 × 4
= 400