Three persons$\mathrm{X}, \mathrm{Y}, \mathrm{Z}$ run on a circular track of length $1 \mathrm{Km}$. at speeds of $20 \mathrm{m}/\mathrm{s}, 40 \mathrm{m}/\mathrm{s}$, and $60 \mathrm{m}/\mathrm{s}$ respectively in the same direction.

If they start running simultaneously, after how much time (in seconds) will they meet again?

Three persons $\mathrm{X}, \mathrm{Y}, \mathrm{Z}$ run on a circular track of length $1 \mathrm{Km}$. at speeds of $20 \mathrm{m}/\mathrm{s}, 40 \mathrm{m}/\mathrm{s} \mathrm{and} 60 \mathrm{m}/\mathrm{s}$ respectively in the same direction.

After how much time will they meet at the starting point ?

John's office is $80 \mathrm{km}$ from his house. One day he started from home, an hour later than his usual time of leaving for his office. In order to cover up the delay, he increased his speed by $4 \mathrm{kmph}$ and thus reached the office on time. Now answer the following questions:

What is the final speed of John?

John's office is$80 \mathrm{km}$ from his house. One day he started from home, an hour later than his usual time of leaving for his office. In order to cover up the delay, he increased his speed by$4 \mathrm{kmph}$ and thus reached the office on time. Now answer the following questions:

84. What is the percentage increase in John's speed?