兩條方程 要列埋步驟 急!! 15點.

第一條
If the value of x after increased by 40% is equal to the sum of 2500 and the value of x after decreased by 10%,find the value of x after decreased by 20%.
x(1+40%)=2500+x(1-10%)
1.4x=2500+0.9x
0.5x=2500
x=5000
∴The value of x after decreased by 20%=5000x(1-20%)=4000

第二條
During the big sale of a department store, all the goods are sold at a discount of 10%. If the marked price of a television set is $11000 and the profit per cent is 10%,find the cost of the televison set.
The selling price of the television set=11000x(1-10%)=$9900.
Let $x be the cost price.
[(9900-x)/x]x100%=10%
(9900-x)/x=0.1
9900-x=0.1x
1.1x=9900
x=9000
∴The cost of the television set is $9000.