Question

The balance of Chiaki's average balance checking account at the beginning of the last cycle was $100, and the only transaction for the cycle was a check that Chiaki wrote for $20, which cleared exactly halfway through the cycle. On what amount did Chiaki's checking account pay interest last cycle?

Answer 1

The correct answer is $90

Answer 2

She had $100 for the first half through the cycle.

Chiaki wrote a cheque for $20.

Now she had $80 for the second half through the cycle.

Therefore:

Amount = (1/2) × 100 + (1/2) × 80 

Amount = 50 + 40 

Amount = $90