Question

David and Eric each shot 6 arrows at the target shown. David shot 4 arrows into A and 2 into B. His score was 18 points. Eric shot 3 into A and 3 into B. His score was 21 points. How many points were given in an arrow in B?

Answer 1

Lets write an equation for each guy's shots and score:
4A + 2B = 18
3A + 3B = 21
To solve we multiply the first equation by -3 and the second by 2:
-12A - 6B = -54
  6A + 6B = 42
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-12A + 0 = -12
A = 1
to find B we substitute in the first equation:
4A + 2B = 18
4(1) + 2B = 18
4 + 2B = 18
2B = 14
B = 7
therefore there were given 7 points in an arrow in B