Asked by Jane

40% of Amy's stamps is equal to 75% of Mary's stamps. After Mary has given 25% of her stamps away , Amy has 90 more stamps than Mary.
Find the total number of stamps they have at first
Answered by Steve
.4a = .75m
.75m = a-90

Now just find a and m, and thus a+m
Answered by Reiny
mary's stamps --- m
Amy's stamps ---- a

.4m = .75a
40m = 75a
m = 75a/40 = 15a/8

after giveaway
Mary has .75m
Amy has a + .25m

a + .25m - .75m = 90
a - .5m = 90
2a - m = 180
2a - 15a/8 = 180
16a - 15a = 1440
a = 1440
m =2700

check my arithmetic
Answered by Steve
Hmmm. I get
a=150
m=80

check:
40% of 150 = 60
75% of 80 = 60

80-20 = 60
150 = 60+90

Extra credit: where did Reiny go wrong?
Answered by Reiny
looks like I can't tell Mary and Amy apart.
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