Question 754391
A piggy bank contains exactly $50 in $1 and $2 coins.
Fanny counted 30 coins.
Frank counted 31 coins.
Who's right?
------------------
n = $1 coins
t = $2 coins
---- 
n + t = 30
n + 2t = 50
------------- Subtract
-t = -20
20 $2 coins
10 $1 coins
Total $50
================
n + t = 31
n + 2t = 50
------------- Subtract
-t = -19
19 $2 coins
12 $1 coins
Total $50
Could be either way.