Question

**Question 5** You look at 50000 past transactions of a convenience store. 225 had a chocolate bar. 489 had gum. 112 had both.

a. You pick one transaction at random from this list to audit. What's the probability that gum was part of this transaction?

**Response:**

b. The first item listed on the receipt of the transaction you picked turns out to be a chocolate bar. Now what's the probability that gum was part of this transaction?

**Response:**

c. What's the "lift" of the association between gum and chocolate bars? Explain what this number means in simple terms (there's multiple ways of interpreting this number; you only need to provide one).

**Response:**

Answer 1

5.

P(gum) = 489/50000

= 0.00978

6.

P = 112/225

= 0.4978

7.

Lift = P(Gum and Chocolate)/P(gum)*P(chocolate)

= 112*50000/489*225

= 50 > 1

A lift value greater than 1 indicates that the gum and chocolate appear more often together than expected, this means that the occurrence of the gum has a positive effect on the occurrence of the chocolate.

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