Question

How do you do this problem?

Answer 1

Remark

You don't need to know anything about the other three numbers. All you need to know is that a is 25% bigger than their sum.

So a + (sum of the three numbers) = 783

Sum of three numbers + 25%(sum of three numbers) = a

sum of three numbers + 1/4 sum of three numbers = a

5/4 (sum) = a Multiply both sides by 4/5 so the left side becomes 1(sum)

5/4 * 4/5 = 4/5 a

a + 4/5a = 783

a(1 + 4/5) = 783

a(1 + 0.8) = 783

a*1.8 = 783

a = 783/1.8

a = 435 Answer

Answer 2

You make use of the given relationships to write an equation only involving "a".

... a = (sum of three numbers) × (1 + 0.25) . . . . a is 25% more than the sum of three numbers.

Then

... (sum of three numbers) = a/1.25 = 0.8a

The sum of the three numbers and a is given as 783.

... sum of 4 numbers = (sum of three numbers) + a

... 783 = 0.8a + a = 1.8a

... 783/1.8 = a = 435

The appropriate selection is (B) 435.