Explanation:
First, Convert the temperature to Kelvin using K = oC + 273
K = 20.0oC + 273
K = 293 K.
Plug in the initial volume, initial temperature, and final volume in the equation V1xT1=V2xT2
4.00 X 293 = 2.00 X T2
Solve for T2:
4.00 X 293 = 2.00 X T2
1172= 2.00T2
1172 ÷ 2.00 = 2.00T2÷ 2.00
586 = T2
The previous answer tells you what it will decrease to, so the total decrease will be the initial temperature - the final temperature:
1172 - 586 = 586
The temperature decreases by 586K