GRE Numeric Entry Sample Questions

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1. Question :

A light bulb blinks at 12 noon. It then blinks after 4 seconds, then after 8 seconds, then after 12 seconds and
so on. How many times shall it have already blinked until it blinks at12.08pm?

Correct Answer:

15

Explanation:

The seconds after which the light bulb blinks are 0, 4, 8, 12 …These form an AP with common difference
4 and first term 0.

Let the number of times it blinks in 8 minutes be n.

Sum of n terms=8*60=480

Sum of n terms in an AP where a is the first term and d is the common difference is given by

Sn=(n/2)[2a+(n-1)d]

(n/2)[2*0+4(n-1)]=480

2n^2-2n-480=0

n^2-n-240=0

n^2-16n+15n-240=0

n(n-16)+15(n-16)=0

n=16

The bulb had already blinked 15 times before it blinked at 12.08 pm

2. Question :

The weight of a woman reduces by 10% every year. If she weighs 100kg today, then after how many years will her
weight be 72.9 kg?

Correct Answer:

3 years

Explanation:

This problem is similar to a compound interest problem where the rate is negative. Let the number of years be
n.

Weight=100(1-10/100)^n=72.9

100(0.9)^n=72.9

(0.9)^n=0.729

n=3

Her weight will be 72.9 kg after 3 years

3. Question :

The LCM of 3/4, 5/6 and 7/8 is …./2. Fill in the blank with the appropriate number.

Correct Answer:

105

Explanation:

LCM of 3, 5 and 7=3*5*7=105

HCF of 4, 6 and 8=2

Required LCM=105/2

The number to be filled in the blank is 105

GRE Numeric Entry Sample Questions

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