This is a question with the concept of Debit and Credit
lets take "+" as what A has in hand
A borrow 50 bucks each from B&C = 50 + 50 = 100
now, in the value of +100
A bought a pair of shoes which cost 97 bucks, and this is in the +100
which means the total value now consist of 97 (owns) & remaining 3 bucks (owns) = 97 + 3 = +100
it is just the transformation of money into an item
Since A return one buck to each of them
He now owe each of them 49 bucks
so, deduct 1 buck each from +100
100 - 1 - 1 = 98 = what he still owes B&C = 49 + 49
it is a balance of what he owns (97+1) and what he owes (49+49)
there is no missing money
or put it in an easier way
since A will return 1 buck each to B&C
tht means if from the beginning A only borrow 49 each
he owes 98
and he bought the shoes with 97 bucks
and he has 1 buck left
tht make perfect sense
the question is just trying to trick us with this : -
"$98在加上A身上的$1 ($98 + $1 = $99)"
this equation is wrong
$98 and $1 is not at the same side at all
because $98 is what he OWES while $1 is what he OWNS
