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If 893 × 78 = p, which of the following is equal to 893 × 79?

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If 893 × 78 = p, which of the following is equal to 893 × 79?  [#permalink]

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New post 14 Oct 2015, 21:20
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A
B
C
D
E

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89% (00:31) correct 11% (00:38) wrong based on 1041 sessions

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Re: If 893 × 78 = p, which of the following is equal to 893 × 79?  [#permalink]

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New post 14 Oct 2015, 21:22
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Bunuel wrote:
If 893 × 78 = p, which of the following is equal to 893 × 79?

(A) p + 1
(B) p + 78
(C) p + 79
(D) p + 893
(E) p + 894


Kudos for a correct solution.

Given: 893 x 78 = P

893 x 79 = 893 x (78 + 1)
= (893)(78) + (893)(1)
= P + 893
= D

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Re: If 893 × 78 = p, which of the following is equal to 893 × 79?  [#permalink]

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New post 14 Oct 2015, 22:13
893x79= 893x(78+1)
= 893x 78 + 893x1
= p+ 893
Answer D
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Re: If 893 × 78 = p, which of the following is equal to 893 × 79?  [#permalink]

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New post 15 Oct 2015, 00:32
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Given: 893 * 78 = p;

To Find: 893 * 79?

893 * 78 = p ---- Eq. 1
893 * 79 = 893 * (78+1) = 893*78 + 893*1 ---Eq. 2 Substituting Eq 1 in Eq 2 (893*78=p)
Hence,
p+893

Answer D; p+893
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Re: If 893 × 78 = p, which of the following is equal to 893 × 79?  [#permalink]

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New post 15 Oct 2015, 01:16
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Forget conventional ways of solving math questions. In PS, IVY approach is the easiest and quickest way to find the answer.



If 893 × 78 = p, which of the following is equal to 893 × 79?

(A) p + 1
(B) p + 78
(C) p + 79
(D) p + 893
(E) p + 894




Since 893 × 78 = p and 79=78+1, we have 893 × 79 = 893 ×(78+1)=893×78 + 893 ×1 = p + 893.

The answer is (D).
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Re: If 893 × 78 = p, which of the following is equal to 893 × 79?  [#permalink]

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New post 15 Oct 2015, 20:33
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893*78=p (given)
893*79 = 893*(78+1)
78=p/893
893*(p/893+1)
=p+893
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Re: If 893 × 78 = p, which of the following is equal to 893 × 79?  [#permalink]

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New post 30 Mar 2016, 20:02
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No need to do all these steps if you are clear about the concept of multiplication you can straight away mark the answer within 10 seconds. We know that any constant number multiplied by increment of 1 actually adds the same constant to the previous result. For instance 4*2 = 8
4*3 = 12 which is 8 from previous result + constant 4 which is being multiplied everytime. Multiplication is repeated addition. Hence answer is p+893
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Re: If 893 × 78 = p, which of the following is equal to 893 × 79?  [#permalink]

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New post 30 Mar 2016, 20:02
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No need to do all these steps if you are clear about the concept of multiplication you can straight away mark the answer within 10 seconds. We know that any constant number multiplied by increment of 1 actually adds the same constant to the previous result. For instance 4*2 = 8
4*3 = 12 which is 8 from previous result + constant 4 which is being multiplied everytime. Multiplication is repeated addition. Hence answer is p+893
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Re: If 893 × 78 = p, which of the following is equal to 893 × 79?  [#permalink]

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Re: If 893 × 78 = p, which of the following is equal to 893 × 79?  [#permalink]

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New post 06 May 2018, 06:13
I have a doubt in Option E
So P+894= 893*78+894 = (893*78)+ (893+1)=893(78+1)=893*79
Im sure that there is some mistake with the method that i followed above but Im not understanding where am i going wrong because if you back solve from the above method 893(78+1)=893*78+893. Can someone help ?
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Re: If 893 × 78 = p, which of the following is equal to 893 × 79?  [#permalink]

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New post 06 May 2018, 13:40
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longhaul123 wrote:
I have a doubt in Option E
So P+894= 893*78+894 = (893*78)+ (893+1)=893(78+1)=893*79
Im sure that there is some mistake with the method that i followed above but Im not understanding where am i going wrong because if you back solve from the above method 893(78+1)=893*78+893. Can someone help ?


There's a problem where you get 893(78+1)=893*79

You are correct to say that P+894= 893*78+894 = (893*78)+ (893+1)
However, the next step cannot be the one you took
You are treating (893+1) as though it were (893*1)

Notice that if we have (893*78)+ (893*1), then we can factor out the 893 to get: (893*78)+ (893*1) = 893(78 + 1)
However, If we have (893*78) + (893+1), we cannot factor out the 893 (as I did above)

Does that help?

Cheers,
Brent
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Re: If 893 × 78 = p, which of the following is equal to 893 × 79? &nbs [#permalink] 06 May 2018, 13:40
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