The price of a personal computer was 42,000 last year. If there is a decrease of

15%, what is the price of the personal computer this year?

You'll calculate the amount it was decreased by:

15% is also 15/100

15/100 * 42000

The two 0's in 100 cut 2 of the 0's in 42000 making it:

15/1 * 420

15 * 420 = 6300

So, 6300 is the amount that the price is decreased by, but the question says the price of the PC (personal computer) after the decrease has happened not the price it decreased by:

So,

42000 - 6300 = 35700.