Câu 1:
a.
$28,5\times 1,5=42,75$
b.
$15,3+20+64,7=35,3+64,7=100$
c.
$4,25\times 57,43-325+42,57\times 4,25$
$=4,25\times (57,43+42,57)-325$
$=4,25\times 100-325=425-325=100$
d.
$\frac{12}{50}+8\text{%}+\frac{59}{100}+9\text{%}$
$=\frac{24}{100}+\frac{8}{100}+\frac{59}{100}+\frac{9}{100}$
$=\frac{24+8+59+9}{100}=\frac{100}{100}=1$
Câu 4:
$BH=BC:2=10:2=5$ (cm)
$S_{BHDA}=(BH+AD)\times AB:2=(5+10)\times 10:2=75$ (cm2)
b.
$AE=AB:2=10:2=5$ (cm)
$S_{AHE}=AE\times BH:2=5\times 5:2=12,5$ (cm2)
S_{AHD}=AD\times AB:2=10\times 10:2=50$ (cm2)
Câu 3:
Hai xe đi từ lúc xuất phát đến khi gặp nhau hết:
$114:60=1,9$ (giờ)
Hai xe đến C lúc:
6 giờ + 1,9 giờ = 6 giờ + 1 giờ 54 phút = 7 giờ 54 phút
b.
Độ dài quãng đường BC: $1,9\times 45=85,5$ (km)
Độ dài quãng đường AB: $114-85,5=28,5$ (km)
Câu 5:
$A=1-\frac{1}{2}+1-\frac{1}{6}+1-\frac{1}{12}+1-\frac{1}{20}+1-\frac{1}{30}+1-\frac{1}{42}+1-\frac{1}{56}+1-\frac{1}{72}+1-\frac{1}{90}$
$=(1+1+....+1)-(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{72}+\frac{1}{90})$
$=9-(\frac{2-1}{1\times 2}+\frac{3-2}{2\times 3}+\frac{4-3}{3\times 4}+...+\frac{9-8}{8\times 9}+\frac{10-9}{9\times 10})$
$=9-(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10})$
$=9-(1-\frac{1}{10})=9-1+\frac{1}{10}=8+0,1=8,1$
Câu 2:
a.
$x+9,44=18,36$
$x=18,36-9,44$
$x=8,92$
b.
$2012:x+23=526$
$2012:x=526-23=503$
$x=2012:503$
$x=4$
c.
$(x-\frac{1}{2})\times \frac{5}{2}+\frac{1}{2}=\frac{7}{4}$
$(x-\frac{1}{2})\times \frac{5}{2}=\frac{7}{4}-\frac{1}{2}=\frac{5}{4}$
$x-\frac{1}{2}=\frac{5}{4}: \frac{5}{2}=\frac{1}{2}$
$x=\frac{1}{2}+\frac{1}{2}=1$
