Brock is training for a Crossfit competition. He began the training by completing pull-ups and box jumps. Originally, his training plan had him completing pull-ups and box jumps at a ratio of 5:4. After two months of training, he decided to focus on his leg strength and adjusted his ratio to 2:7. If he completed 53 box jumps at the end of his training, how many pull-ups did he complete in the initial stage of training?

Answer:Brock completed approximately 38 pull ups in the initial stage of training.         Step-by-step explanation: We are given the following information in the question: Ration of pull ups and box jumps initially = [tex]\displaystyle\frac{5}{4}[/tex]   Ration of pull ups and box jumps later = [tex]\displaystyle\frac{2}{7}[/tex]     Number of box jumps completed in the end of training = 53Total number of exercises done in the end = 2x + 7x = 9x We use the concept of ratio.[tex]7x = 53\\\\=x = \displaystyle\frac{53}{7}\\\\\Rightarrow 2x = \frac{106}{7}\\\\\Rightarrow \text{Total number of excercise} = \frac{477}{7}[/tex]Initially,Total number of exercise = 5y + 4y[tex]9y = \displaystyle\frac{477}{7}\\\\\Rightarrow y = \frac{477}{63}\\\\\Rightarrow \text{Pull ups done initially} = 5y = 5\times \frac{477}{63} = 37.85 \approx 38[/tex]Thus, he completed approximately 38 pull ups in the initial stage of training.