Đáp án:
BẠN THAM KHẢO NHA!
Giải thích các bước giải:
Bài 1:
$a, 66.25+5.66+66.14+33.66$
$=66.(25+5+14+33)$
$=66.77=5082$
$b,48.19+48.115+134.52$
$=48.(19+115)+134.52$
$=48.134+134.52$
$134.(48+52)$
$134.100=13400$
Bài 2:
$S1=1+2+3+...+999$
$=\dfrac{(999+1).(\dfrac{999-1}{1}+1)}{2}$
$=499500$
$S6=15+25+35+...+115$
$=\dfrac{(115+15).(\dfrac{115-15}{10}+1)}{2}$
$=715$
$S7=24+25+26+...+126$
$=\dfrac{(126+24).(\dfrac{126-24}{1}+1)}{2}$
$=7725$