If a is a 3-digit integer and b is a 3-digit integer, is the units

Question

If  a  is a 3-digit integer and  b  is a 3-digit integer, is the units digit of the product of  a  and  b  greater than 5?

(1) The units digit of  a  is 4.
(2) The units digit of  b  is 7.

pushpitkc · Accepted Answer

Since we have been asked to find if the units digit of the product of the numbers 
is greater than 5, knowing the units digit of both the numbers is enough to determine that.

(1) The units digit of  a  is 4.
Since, we have no idea about the units digit of the number b, we cannot clearly tell
if the units digit of product is greater than 5. Insufficient
(2) The units digit of  b  is 7.
Since, we have no idea about the units digit of the number a, we cannot clearly tell
if the units digit of product is greater than 5. Insufficient

On combining both the statements, it is clear that the units digit of their product is 8(>5)
Hence, sufficient(Option C)

BrentGMATPrepNow · Answer

Target question :    Is the units digit of the product of  a  and  b  greater than 5?

Given :  a  is a 3-digit integer and  b  is a 3-digit integer

Statement 1 : The units digit of  a  is 4   
There are several values of a and b that satisfy statement 1. Here are two: 
Case a: a = 104 and b = 102. In this case the product ab = (104)(102) = ---- 8 . So,  the units digit of ab IS greater than 5 
Case b: a = 104 and b = 100. In this case the product ab = (104)(100) = ---- 0 . So,  the units digit of ab is NOT greater than 5 
Since we cannot answer the  target question  with certainty, statement 1 is NOT SUFFICIENT

ASIDE: When I write that the product ab = (104)(102) = ---- 8 , I'm ignoring all digits in the product OTHER THAN the units digit, since that's all we care about.

Statement 2 : The units digit of  b  is 7  
There are several values of a and b that satisfy statement 2. Here are two: 
Case a: a = 104 and b = 107. In this case the product ab = (104)(107) = ---- 8 . So,  the units digit of ab IS greater than 5 
Case b: a = 100 and b = 107. In this case the product ab = (100)(107) = ---- 0 . So,  the units digit of ab is NOT greater than 5 
Since we cannot answer the  target question  with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined    
Statement 1 tells us that a = -- 4 
Statement 2 tells us that b = -- 7 
So, ab = (-- 4 )(-- 7 ) = ----- 8 
So,  the units digit of ab IS greater than 5 
Since we can answer the  target question  with certainty, the combined statements are SUFFICIENT

Answer:  C

Cheers,
Brent

MarkusKarl · Answer

We need to find the unit digits of both (or one if its 0).

I - 4 multipels can generate 4 or 8 as two examples - no need to look further. NS

II - 7 multipels can generate 7 or 14, 7>5; 4<5. NS

Together:
4*7=28 8>5. Sufficient.
C

Posted from my mobile device

RaguramanS · Answer

If a is a 3-digit integer and b is a 3-digit integer, is the units digit of the product of a and b greater than 5?

Unit digit of A*B>5 
Let x,y = unit digit of a and b

(1) The units digit of a is 4.
If y=2, x*y= 8
If y=1, x*y= 4
 NS

(2) The units digit of b is 7
If x= 3, x*y = 21 ( unit digit is 1)
If x= 4, x*y = 28 ( unit digit is 8)
 NS

St 1+2. Suff x*y= 28 ( unit digit is 8 )

Option C

akshayk · Answer

a = xyz
b = def
z*f = gh , where h is the unit's digit of  z*f 
=> h > 5 ?

1) z = 4, f = 1
z*f = 4 => h = 4
NO
But z = 4, f = 2
z*f = 8 => h = 8
YES
Insufficient.

2) f = 7, z = 1
f*z = 7 => h = 7
YES
But, z = 2, f = 7
f*z = 14 => h = 4
NO
Insufficient

1+2)
f = 7 , z = 4
z*f = 28
h > 5 => YES
Sufficient.

C is the answer.

ScottTargetTestPrep · Answer

We are given that a is a 3-digit integer and b is a 3-digit integer and need to determine whether the product of a and b is greater than 5.

Statement One Alone:

The units digit of a is 4.

Statement one alone is not sufficient to answer the question. For example, if the units digit of b is 1, then the units digit of the product of a and b is 4, which is less than 5; however, if the units digit of b is 2, then the units digit of the product of a and b is 8, which is greater than 5.

Statement Two Alone:

The units digit of b is 7.

Statement two alone is not sufficient to answer the question. For example, if the units digit of a is 1, then the units digit of the product of a and b is 7, which is greater than 5; however, if the units digit of a is 0, then the units digit of the product of a and b is 0, which is less than 5.

Statements One and Two Together:

Using the information from statements one and two, we see that since the product of the units digits of a and b is 4 x 7 = 28, the units digit of the product of a and b is 8, which is greater than 5.

Answer: C

GMATinsight · Answer

Answer: Option C

Video solution by  GMATinsight

https://www.youtube.com/watch?v=LSgGR4KFSVo

NightWalker · Answer

Let a= xyz and b= abc

Units digit of the product of the numbers above will have component of z*c
therefore, question is the unit digit of z*c >5

C: Both statements are necessary.

avigutman · Answer

Video solution from Quant Reasoning: Subscribe for more: https://www.youtube.com/QuantReasoning? ... irmation=1 https://www.youtube.com/watch?v=tD2K35tg3OA

bumpbot · Answer

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If a is a 3-digit integer and b is a 3-digit integer, is the units

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