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1. A cyclist traveled 45 miles in x hours. Her average speed was 2x-1 mph. If her speed was constant, how far in miles, did she travel in two hours? 2. What is the average (arithmetic mean) of 3a+7 and 4a+1?

最佳解答:

1. A cyclist traveled 45 miles in x hours. Her average speed was 2x － 1 mph. If her speed was constant, how far in miles, did she travel in two hours? Sol: hint ~ distance ＝ speed * time 45 ＝ x * ( 2x － 1 ) 2x2 － x ＝ 45 2x2 － x － 45 ＝ 0 ( 2x ＋ 9 ) ( x － 5 ) ＝ 0 x ＝ 5 or x ＝ - 9 ( x ＞ 0, therefore x ＝ - 9 rejected ) 5 * 2 ＝ 10 Ans: 10 miles 2. What is the average (arithmetic mean) of 3a + 7 and 4a + 1 ? Sol: [( 3a +7)+( 4a +1)]/2 ＝ ( 7a +8)/2 ＝ 7a/2 ＋ 4 Ans: 7a/2 ＋ 4 Send me a letter if any steps you don’t understand.

其他解答:

1. 10 miles 2. 2a + 4
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