Kevin is a fruit vendor. He always sells a total of 50 crates of fruit per week. Last week he sold 13 crates of grapes, 20 crates of mangoes, and the rest were passion fruits. How many passion fruit crates did he sell? Think carefully first, then make a decision:
Between grapes and mangoes, we have 13 + 20 = 33 crates. The remaining crates are passion fruits, so we have 50 - 33 = 17 crates of passion fruit. So, the answer is 17.