The formula to use is:
percent change = 100*(b-a)/a
where,
a = start value
b = end value
The b-a up top represents the change from a = 60 to b = 24
This is a change of -36 since b-a = 24-60 = -36
The negative result indicates a percent decrease.
Divide this change over the original amount a = 60 to get -36/60 = -0.60
Then we multiply by 100 to convert to a percentage.
It is equivalent to moving the decimal point 2 spots to the right.
0.60 becomes 60%
Here is the calculation in one line
100*(b-a)/a = 100*(24-60)/60 = -60
Then erase the negative sign and stick on a percent sign at the end.
Check:
60% of 60 = 0.60*60 = 36
Decreasing by 60% means we lose 36, so 60-36 = 24 which confirms we have the correct answer.
Another way to check:
If you get a 60% discount then you pay the remaining 40%
The start price $60 becomes 0.40*60 = 24 dollars
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