Andres bought exactly two sorts of donuts, old-fashioned donuts and jelly donuts. If each old-fashioned donut costs

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

by BTGmoderatorDC » Mon Jul 13, 2020 7:16 pm

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Andres bought exactly two sorts of donuts, old-fashioned donuts and jelly donuts. If each old-fashioned donut costs $0.75 and each jelly donut costs $1.20, how many jelly donuts did Andres buy?

(1) Andres bought a total of eight donuts.
(2) Andres spent exactly $7.35 on donuts.

OA B

Source: Magoosh

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Source: Beat The GMAT — Data Sufficiency | Mon Jul 13, 2020 7:16 pm

deloitte247: Legendary Member; Posts: 2214; Joined: Fri Mar 02, 2018 2:22 pmFollowed by: 5 members

Re: Andres bought exactly two sorts of donuts, old-fashioned donuts and jelly donuts. If each old-fashioned donut costs

by deloitte247 » Fri Jul 17, 2020 8:03 am

Let old fashioned donuts = o and jelly donuts = j
Cost of o = $0.75
Cost of j = $1.20

Target question => How many jelly donuts did Andres buy?

Statement 1 => Andres bought a total of eight donuts
i.e o + j = 8; value of o and j is unknown. There are lots of variations that could satisfy the statement but will not provide a definite answer to the target question. Hence statement 1 is NOT SUFFICIENT.

Statement 2 => Andres spent exactly $7.35 on donuts since cost of o and j = $0.75 and $ 1.20 respectively
(0.75 * o) + (1.20 * j) = 7.35
0.75o + 1.20j = 7.35
(0.75o * 100) + (1.20j * 100) = (7.35 * 100)
75o/15 + 120j/15 = 7.35/15
50 + 8j = 49 .........eqn 1
By testing with numbers > or = 1, the only set of value that satisfies the equation above is when o = 5and j = 3
50 + 8j = (5 * 5) + (8 * 3)
=25 + 24 = 49

Statement 2 alone is SUFFICIENT
Answer = B

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

Re: Andres bought exactly two sorts of donuts, old-fashioned donuts and jelly donuts. If each old-fashioned donut costs

by swerve » Fri Jul 17, 2020 11:00 am

BTGmoderatorDC wrote: ↑
Mon Jul 13, 2020 7:16 pm
Andres bought exactly two sorts of donuts, old-fashioned donuts and jelly donuts. If each old-fashioned donut costs $0.75 and each jelly donut costs $1.20, how many jelly donuts did Andres buy?

(1) Andres bought a total of eight donuts.
(2) Andres spent exactly $7.35 on donuts.

OA B

Source: Magoosh

1) Andres bought a total of eight donuts.
$O+J=8$. Not sufficient $\Large{\color{red}\chi}$

2) Andres spent exactly $7.35 on donuts.
$0.75 \cdot O + 1.2 \cdot J = 7.35$
$75 O + 120 J = 735$
$5 O + 8 J = 49$
$O=5, J=3$ only one set of values satisfies this equation $\Large{\color{green}\checkmark}$

Therefore, B

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