Well, the numerator is the number on top, so in the fraction 3/5, 3 is the numerator. To find the equation with a denominator of 30 that is equivalent, find what the difference is. 30/5 = 6. So now, multiply the numerator by 6. 6 * 3 = 18. The new fraction is 18/30. The numerator is 18. Hope this helps!
This is the concept of speed: ω=600 rev/min=600*2π rad/min=1200 rad/min v=rω=70*1200π =84,000 in/min converting the above in miles per hour we get: 84000 in/min =(84000*1.6*10^(-5)*60) =80.64 mph
