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posted by Speedo .
The 23rd term in a certain geometric sequence is 16 and the 28th term in the sequence is 24. What is the 43rd term?
It is not 48.

a+22d = 16
a+27d = 24
a = 96/5
d = 8/5
96/5 + 42*8/5 = 96/5 + 336/5 = 240/5 = 48
If 48 is marked wrong, the key is in error. You could have checked it yourself. 
This is what you did wrong, i think. YOu multiply not add.

Or, look at it this way. From T23 to T28 is 5 terms, and the value grew by 8.
From T28 to T43 is 15 terms = 3*5, so the value will grow by 3*8, or 24.
24+24 = 48