Similarly, the third number is (x+4)/4, and the fourth number is 4*(x+4).
x+(x+8)+(x+4)/4+4 *(x+4)= 100
The solution is x= 12.
The first number is 12, the second number is 20, the third number is 4 and the fourth number is 64.
2. Set the purchase price to X yuan.
( 1)x+x*50%= 180，x= 120。
(2)x+x* 100%= 180 gives x=90.
So the purchase price of this dress should be between 120 yuan -90 yuan.
If you make a counter-offer at 20% of the purchase price, it will be 90+90*20%= 135,120+120 * 20% =144.
So the counter-offer should be between 135 yuan and 144 yuan.
3.( 1)a * 0.40+(84-a)* 0.40 * 70% = 30.72
The solution is a=60.
(2) Let the electricity consumption in June be X degrees.
0.36*x=0.40*60+(x-60)*0.40*70%
The solution is x= 105.
105*0.36=37.8
So he used 105 kwh of electricity in June and paid 37.8 yuan for electricity.