Phone call is billed as: x+x+x+x+x+ x/2 + x/2 + ... = 100cents

1. If he had spoken for another minute, he would have paid 10 cents more

If he talked for 1min, x=100. So, 2nd min will be charged at 100, not 10.

If he talked for 2min, 2x=100 => x=50. So, 3rd min will be charged at 50, not 10.

If he talked for 4min, 4x=100 => x=25. So, 5th min will be charged at 25, not 10.

If he talked for 5min, 5x=100 => x=20. So, 6th min will be charged at 20/2 = 10.

Sufficient.

2. If he had spoken for one minute fewer, he would have paid 20 cents fewer.

Working as above, if he talked for 5mins, at 4mins he paid 20 cents fewer.

Sufficient.

Ans: D

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