OLD                            New

200 mA                        _____mA

0.5 sec                           0 . 5 sec

70 kVp                           80 kVp

72"SID                          40"SID

200 screen                    400 screen

#1 Find mAs

#2 15 % rule

#3 new distance/old distance squared

#4 old screen/new screen

#5  final mAs divided by time

#1 200mA x 0.5 sec = 100mAs

#2 100mAs divided by 2 = 50mAs

#3  40/72 squared =  1600/5184 = 0.31    

    50mAs x 0.31 = 15. 5 mAs

#4  200/400 = 0.5

    15.5mas x 0.5= 7.75

#5 7.75 divided by .5 =15.5 mA (SORRY ABOUT THE WEIRD NUMBER!!!!)