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If x and y are positive integers, what is the result when the units digit of (5x−3)6+y is divided by 10 ?

(1) y=4

(2) x=5

Question stem:
(5x−3)6+y = 30x -18 + y
\(\frac{rem(30x -18 + y)}{10}\)= \(\frac{rem(0 -8 + y)}{10}\)
if we know the value of y, we know the remainder.

statement 1:
y = 4
sufficient

statement 2:
x =5
not sufficient

Ans: A
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Quote:
If x and y are positive integers, what is the result when the units digit of (5x−3)6+y(5x−3)6+y is divided by 10 ?

(1) y=4
(2) x=5

(5x-3)6+y
x=1: 5-3=2*6=12+y
x=2: 10-3=7*6=42+y
x=3: 15-3=12*6=72+y
notice pattern: units=[2]+[units of y]

(1) sufic

result: [2]+[4]/10=6/10

(2) insufic

Ans (A)
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If x and y are positive integers, what is the result when the units digit of (5x−3)6+y is divided by 10 ?
\(\frac{(5x−3)6+y}{10} = \frac{30x + y - 18}{10}\)
Unit Digits(\(\frac{30x}{10} + \frac{y}{10} - \frac{18}{10}\)) = x + y - 8
So, we need x + y = ?

(1) y=4
INSUFFICIENT.

(2) x=5
INSUFFICIENT.

Together 1 and 2
x + y = 9

SUFFICIENT.

Answer C.
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If x and y are positive integers, what is the result when the units digit of (5x−3)6+y is divided by 10 ?

(1) y=4

(2) x=5
stem: the value of 5x-3 will always be 2, if x is positive integer.
so unit's digit will always be 2*6 = _2...depends only on value of y
1) units digit will be 6, so remainder is 6
sufficient
2) insufficient
Ans A
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unit's digit (5x−3)6+y is divided by 10

(1) y=4.........SUFFICIENT

whatever the value of x.... the units digit of the product (5x−3)6 is 2......so 2+4=6

(2) x=5.........CLEARLY INSUFFICIENT

OA:A
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(5x - 3)6 + y mod 10 = (30x -18 +y) mod 10 = (y-2) mod 10

1) y= 4
(y-2) mod 10 = 2
SUFFICIENT

2) x = 5
Since (y-2) mod 10 is independent of x.
NOT SUFFICIENT

IMO A

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How is result synonymous with remainder?
Bunuel

Competition Mode Question



If x and y are positive integers, what is the result when the units digit of \((5x − 3)6 + y\) is divided by 10 ?

(1) \(y = 4\)

(2) \(x = 5\)
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inayat2643
How is result synonymous with remainder?
Bunuel

Competition Mode Question



If x and y are positive integers, what is the result when the units digit of \((5x − 3)6 + y\) is divided by 10 ?

(1) \(y = 4\)

(2) \(x = 5\)

It's not synonymous. We need the result when the units digit of \((5x − 3)6 + y\) is divided by 10. From (1), the units digit comes out to be 6, so the result is 0.6.
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Understood! Thank you so muchhh.
Bunuel
inayat2643
How is result synonymous with remainder?
Bunuel

Competition Mode Question



If x and y are positive integers, what is the result when the units digit of \((5x − 3)6 + y\) is divided by 10 ?

(1) \(y = 4\)

(2) \(x = 5\)

It's not synonymous. We need the result when the units digit of \((5x − 3)6 + y\) is divided by 10. From (1), the units digit comes out to be 6, so the result is 0.6.
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Any +ve Multiple of 6 will have 6 as a unit digit.

So, only Y's value is required. 1 is sufficient.
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