Question. Before Cameron broke his right arm, he was able to type 10 words per minute on his phone. After he broke his arm, he had to use his left hand for a while, and he could only type 8 words per minute. What is the difference between the number of words he could type in 5 minutes before and after he broke his arm?
Answer. 10
What step-by-step reasoning justifies that answer?
Reasoning: Before Cameron broke his hand he could type 5 × 10 = 50 words in 5 minutes. After he broke his hand he could only type 5 × 8 = 40 words in 5 minutes. The difference between the number of words he could type in 5 minutes before and after he broke his arm is 50 - 40 = 10 words.