Chapter 3.1: Natural Numbers

How many natural numbers are there between 21 and 195?

If we multiply a number by 4 and subtract 7, the result is 69. Find the number.

Answer explanation

6500/100 = 65

9000/1000 = 9

65+9=74

Let A = 1 + 2 + 3 + 4 + ... + 29 + 30, and

B = 2 + 4 + 6 + ... + 28 + 30.

What is A – B?

• 220

• 225

• 450

• 600

Answer explanation

1+2+3+...+30 - 2 -4-...-30=1+3+5+...29=15*15=225