If you want to calculate 7/8 * 216 you can do this without a calculator. Simply look if there are numbers that are both in the numerator and denominator. Since you can divide 216 with 8 you can change the calculation to become 7*(216/8) = 7*((27*8)/8) = 7*27 = 189.
Another way to see if you can easily multiply 7/8 with 216 is to divide 216 in its prime numbers.
216=2*108=2*2*54=2*2*2*27=8*27
7/8*8*27 = 8/8*7*27=7*27=189
We don't need to do further than to the point where we see that the numerator and denominator both contain the same number. Then you simply remove the 8's from the numerator and denominator :)
