math
posted by Evelyn on .
Andy had 20% fewer marbles than Henry. When Andy gave 80 marbles to Henry, the numbers of marbles he had left was half of what Henry had. How many marbles did Andy have in the begining?
Please help me

at start:
Henry  x marbles
Andy  .8x marbles
after giveaway:
Henry  x+80
Andy  .8x  80
Andy's marbles = 1/2 of Henry's marbles
.8x80 = (1/2)(x+80)
times 2
1.6x  160 = x+80
.6x = 240
x = 400
So Henry had 400 and Andy had 320
check: after giveaway
Andy is left with 240
Henry now has 480
Does Andy have half of what Henry has?? YES 
at start:
Henry  x marbles
Andy  .8x marbles
after giveaway:
Henry  x+80
Andy  .8x  80
Andy's marbles = 1/2 of Henry's marbles
.8x80 = (1/2)(x+80)
times 2
1.6x  160 = x+80
.6x = 240
x = 400
So Henry had 400 and Andy had 320
check: after giveaway
Andy is left with 240
Henry now has 480
Does Andy have half of what Henry has?? YES 
400for henry 320 for andy