shreerajp99 wrote:

If 1 book was left when a pile of books was stacked in rows of 5, how many books are there in all?

(1) When the books were stacked in rows of 7, 1 book was left

(2) When the books were stacked in rows of 8, 4 books were left

I solved this using Remainder approach.

From question stmt: N/5

1.N/7 Remainder is 1

so find a number such that when N/5 and N/7 gives remainder of 1. Found N=36.Sufficient

2.N/8 Remainder is 4

so N/5 gives remainder 1 and N/8 gives remainder 4.Found N =36.Sufficient.

Can someone xplain whats wrong with my approach?

B = 5k + 1

STAT1

B = 7t + 1

5k + 1 =7t + 1

k = 7t/5

So, Those values of t which will give you integer value are the common solution.

So, t=5,10,15,20

k = 7,14,21,28,35,42,49,56,63,...

So, B = 36, 71,...

So, Not Sufficient as there are many possible values!

STAT2

B = 8s + 4

5k + 1 = 8s + 4

k = (8s + 3)/5

Those values of s which will give you integer value of k are solution.

s = 4, 9,14,19,24,...

k = 7, 15, 23,31,39, 47, 55, 63

So, B = 36, 76,...

So, Not Sufficient as there are many possible values!

Trying for C

k = 7 and 63 are the two solutions which are possible (actually there are more...)

B = 36, 316

So, Answer is E

Hope it helps!

_________________

Ankit

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How to Solve :

Statistics || Reflection of a line || Remainder Problems || Inequalities