Bunuel wrote:

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.

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 5Case 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 5Since 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 5Case 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 5Since we cannot answer the

target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined Statement 1 tells us that a = --

4Statement 2 tells us that b = --

7So, ab = (--

4)(--

7) = -----

8So,

the units digit of ab IS greater than 5Since we can answer the

target question with certainty, the combined statements are SUFFICIENT

Answer:

Cheers,

Brent

_________________

Brent Hanneson – Founder of gmatprepnow.com