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Explanation:
I'm assuming you meant to say 2 & 1/2 instead of 2,1/2
If so, then we cut that last term 2 & 1/2 in half
The whole part 2 cuts in half to 1
The fractional part 1/2 cuts in half to 1/4
2 & 1/2 cuts in half to 1 & 1/4 which leads to choice C
The reason why we cut in half is because the jump from 20 to 10 is "divide by 2", and the same applies from 10 to 5, and from 5 to 2 & 1/2.
