Remember that if there is a 25% discount, then the amount you are paying represents 75%. We know the original price (ie 100%) There are several methods. Simplest: Find 25% of the$40 and subtract to find the price to be paid. 25 % o f 40 = 25 100 × 40 = 10 discount price = 40 − 10 = $ 30
Second method. Find 75% immediately 75 % o f 40 = 75 100 × 40 = $ 30
You can do any percentage question using the concept of direct proportion. 40 100 = x 75 if $40 is 100%, how much is 75%? 100 x = 75 × 40 cross-multiply
x = 75 × 40 100 this a possible expression for the sale price x = $ 30
We must select a counter-example that makes the conclusion false.
3 is a prime, 5 is a prime, and 7 is a prime. The conclusion is that all odd numbers are prime numbers. A counter example is that 9 is an odd number but it is NOT a prime number.
