So first, we want to find the total decrease on the number.
Since it was first decreased by 50% and then 10%, we can just multiply the two together to find what 10% of 50% is. I find it easier when they're both fractions, or 1/2 and 1/10.
1/2 * 1/10 = 1/20
So one quarter is 1/4, or 5/20.
1/20 is 4/20 less then 5/20.
1/20 is 30 less then 1/4, then 4/20 must equal 30.
4/20 is also 1/5.
So just multiply 30 by 5, to get 150 as your number. (1/5 * 5 = 5/5)
