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Ages & Problems on Numbers · Question 46 of 60

Question 46

MediumOriginal question

The sum of the reciprocals of two consecutive natural numbers is 1130\frac{11}{30}. What is the larger number?

Options for question 46

Show the answer and explanation
CorrectNot quiteAnswer A

Correct answer: A

Explanation

  1. 1x+1x+1=2x+1x(x+1)=1130\frac{1}{x} + \frac{1}{x + 1} = \frac{2x + 1}{x(x + 1)} = \frac{11}{30}.

  2. Match: x(x+1)=30x(x + 1) = 30 and 2x+1=112x + 1 = 11 both give x=5x = 5.

  3. The numbers are 5 and 6, so the larger is 6. Check: 15+16=1130\frac{1}{5} + \frac{1}{6} = \frac{11}{30}.

Worth noting

11 is the SUM of the two numbers (the numerator), and 30 is their product; neither is the larger number.

Concept
Sum of reciprocals of consecutive numbers
Typical time
70 s
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Ten questions from Ages & Problems on Numbers, at your own pace.

Practise this chapter →

Ten questions from Ages & Problems on Numbers, at your own pace.