PrepTest 152 · Section 2 · Question 9

Grandpa's Suspicious Shuffle

Grandpa has a music player with a shuffle button. 'Shuffle means every song gets an equal shot,' he says proudly. Tommy listens all afternoon while he hides candy in the couch. He keeps a tally. Out of twenty songs that play, sixteen come from Grandpa's polka album. 'Grandpa, your shuffle is broken!' Tommy yells. 'It loves polka!' Lulu looks up from her clipboard. 'Wait. How many polka songs are on the playlist in the first place? If almost the whole playlist is polka, then of course polka keeps coming up. That would be fair.' Tommy frowns. Grandpa scrolls through. 'Four albums,' he says. 'Ten songs each. Polka is just one quarter.' Tommy grins. 'Then sixteen out of twenty really is fishy!' Now his case is much stronger.

Grandpa's shuffle is supposed to give every song an equal chance. Yet sixteen of the twenty songs it played came from the polka album. So the shuffle is not fair.

Which choice, if true, gives the most support to Tommy's conclusion?

The Case of the Crooked Coin Toss

In a fictional town, a referee is accused of using a trick coin. 'Your Honor,' says Mr. Whitfield, snapping his suspenders, 'heads came up in nine of ten tosses this season. A fair coin gives heads and tails an equal chance. This coin is rigged.' The other lawyer stands. 'But maybe the home captain always calls heads and wins the toss anyway.' Mr. Whitfield smiles. 'Our expert tested the coin a thousand times in the lab under neutral conditions. Half the time, the toss was supposed to show tails.' The judge nods. 'So the setup was not tilted. That makes your evidence count.' Showing the starting conditions were even is what turns a lopsided result into proof.