The integer x has a tens digit of 6 and a units digit of 7. The units digit of integer y is 8. The product of x and y

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BTGmoderatorDC: Moderator; Posts: 7187; Joined: Thu Sep 07, 2017 4:43 pmFollowed by: 23 members

by BTGmoderatorDC » Tue Nov 03, 2020 5:55 pm

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The integer x has a tens digit of 6 and a units digit of 7. The units digit of integer y is 8. The product of x and y has a tens digit of 8. Which of the following is a possible tens digit of integer y?

A. 3
B. 4
C. 5
D. 6
E. 7

OA C

Source: Veritas Prep

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Source: Beat The GMAT — Problem Solving | Tue Nov 03, 2020 5:55 pm

swerve: Legendary Member; Posts: 2539; Joined: Sun Oct 29, 2017 2:04 pmFollowed by: 6 members

Re: The integer x has a tens digit of 6 and a units digit of 7. The units digit of integer y is 8. The product of x and

by swerve » Wed Nov 04, 2020 3:53 pm

BTGmoderatorDC wrote: ↑
Tue Nov 03, 2020 5:55 pm
The integer x has a tens digit of 6 and a units digit of 7. The units digit of integer y is 8. The product of x and y has a tens digit of 8. Which of the following is a possible tens digit of integer y?

A. 3
B. 4
C. 5
D. 6
E. 7

OA C

Source: Veritas Prep

We can try as follows:

$x=67$
$y=p8$
Multiplying them, we have $(10p+8)\cdot 67 \Rightarrow 670p+536$

Now, checking values
$p=3 \Rightarrow$ Tens digit of the result $=4 \Large{\color{red}\chi}$

$p=4 \Rightarrow$ Tens digit of the result $=1 \Large{\color{red}\chi}$

$p=5 \Rightarrow$ Tens digit of the result $=8 \Large{\color{green}\checkmark}$

Therefore, C

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Re: The integer x has a tens digit of 6 and a units digit of 7. The units digit of integer y is 8. The product of x and

by Scott@TargetTestPrep » Tue Nov 10, 2020 1:10 pm

BTGmoderatorDC wrote: ↑
Tue Nov 03, 2020 5:55 pm
The integer x has a tens digit of 6 and a units digit of 7. The units digit of integer y is 8. The product of x and y has a tens digit of 8. Which of the following is a possible tens digit of integer y?

A. 3
B. 4
C. 5
D. 6
E. 7

OA C

Solution:

We see that a possible value of integer x is 67. If we let the tens digit of y be t, then 10t + 8 is one of the possible value of y, and the product of xy is:

67(10t + 8) = 670t + 536 = 600t + 70t + 500 + 30 + 6 = 100(6t + 5) + 10(7t + 3) + 6

The tens digit of xy is the units digit of the value 7t + 3 and it should be 8. Now let’s check the given answer choices:

A) 7(3) + 3 = 24 → The units digit is not 8.

B) 7(4) + 3 = 31 → The units digit is not 8.

C) 7(5) + 3 = 38 → The units digit IS 8.

Answer: C

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