Question

Bob and Caitlyn are playing a trading-card game. Between them, they have 81 cards. Bob has 7 fewer cards than Caitlyn.

Answer 1

B=c-7 and b+c=81 using b from the first in the second gives you:

(c-7)+c=81

2c-7=81

2c=88

c=44 so b=81-44=37

So Bob has 37 cards and Caitlyn has 44 cards

Answer 2

We know that Bob and Caitlyn are playing a trading-card game. Between them, they have 81 cards. Bob has 7 fewer cards than Caitlyn. Since Bob has 7 cards fewer them Caitlyn we have to divide by 2 and subtract 7. 

81 / 2 = 40 [rounded] 

40 - 7 = cards Bob has 

= 33 cards bob has