Anna can read 1 page in 1 minute. Carole can read as fast as Anna but at half the speed of Brianna. How long does it take Brianna to read a 100-page book? Think carefully first, then make a decision:
If Anna can read 1 page in 1 minute, then her speed is 1 / 1 = 1 page per min. If Carole can read at Anna's same speed then her speed is also 1 page per min. If Carole is only half the speed of Brianna, then that means Brianna is twice as fast as Carole, so 2 * 1 page per min = 2 pages per min. If a book is 100 pages long and Brianna can read 2 pages per minute, then it will take her 100 / 2 = 50 minutes to read the book. So, the answer is 50.