Question

explicati cum se fac aceste exercitii.URGENT VA ROG FRUMOS!!!

Answer 1

1.
240:20%=240 × 100/20=1200

2.
100%+20%=120%
243 :120%=243 ×100/120=202,5 lei pret initial

3.
(1+2+3+...+2004)/(2+4+6+....+2004)=(2x-1)/x
(1+2+3+...+2004)/2(1+2+3+....+1002)=(2x-1)/x
(2004×2005/2)/2(1002×1003/2)=(2x-1)/x
(1002×2005)/(1002×1003)=(2x-1)/x
2005/1003=(2x-1)/x
2005x=2006x-1003
x=1003

4.
P₁/P₂=2/3
4L₁/4L₂=2/3
L₁/L₂=2/3
A₁/A₂=L₁²/L₂²  =(L₁/L₂)²=(2/3)²=4/9

5.
a/b=5/7        b=7a/5
(a+b)/2=29,4     
a+b=58,8   
a+7a/5=58,8
5a+7a=294
12a=294
a=24,5
b=7×24,5/5=34,3

6
a+b=56  
a/b=3/4      b=4a/3
a+4a/3=56
3a+4a=168
7a=168
a=24
b=4×24/3=32

7

100%-15%=85%
1377:85%=1377 ×100/85=1620 lei
 
100%-10%=90%
1620:90%=1620 ×100/90=1800 lei  pret initial