There are 4 people. They average 68, so the total key chains are 68 x 4 = 272.
Tarun has 78, so the other three people have a total of 272 - 78 = 194.
Let Marcus = X
James has half as many as Marcus, so he is 0.5X
Yahya is (x + 0.5x)-28 = 1.5X-28
Now add them together to equal 194:
X + 0.5x + 1.5x -28 = 194
Simplify:
3x -28 = 194
Add 28 to each side:
3x = 222
Divide both sides by 3:
x = 222 / 3
x = 74
Marcus = x = 74 key chains.
James = 0.5x = 0.5(74) = 37 key chains.
Yahya = 1.5x-28 = 1.5(74) -28 = 111-28 = 83 key chains.
Tarun = 78 key chains.
Check: 74 + 37 + 83 + 78 = 272 ( matches the total above).
