Three consecutive whole numbers add up to 78. What is the smallest of the three?

Class 6Whole NumbersWhole Numbers

Step-by-Step Solution

Let the numbers be

n, n + 1, n + 2

. Their sum is

3 n + 3 = 78

, so

3 n = 75

and

n = 25

. The three numbers are 25, 26, 27, and the smallest is 25.

Answer: A) 25

Key idea: Closure: when an operation 'stays inside' the whole numbers

Adding two whole numbers always gives a whole number — addition is **closed** on whole numbers. Multiplying two whole numbers always gives a whole number — multiplication is **closed** too. But subtraction is **not** closed: 5 − 7 = −2, which is not a whole number. Division is also not closed: 7 ÷ 2 = 3.5, not a whole number. Closure is the property that lets us trust an operation never to take us 'outside' the world of whole numbers.

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