Bunuel
An old photograph shows a group of people standing in a row. If 4 of the 10 people from the left are wearing hats and all remaining people in the row are wearing hats, how many people are in the row?
(1) 5 of the 6 people from the right are wearing hats.
(2) 3 of the 8 people from the left are wearing hats.
The Old photograph shows a group of people who are standing in a row.
We need to find the number of people in the row?
Given that 4 out of 10 people from left are wearing hat.
Let the initial ten positions be numbered P1, P2 ..... P10. If we assume the first four members wear hat. And the rest 6 members doesn’t wear hat.
P1, P2, P3, P4 wear hat and the remaining P5 till P10 doesn’t wear hat.
Statement 1:
(1) 5 of the 6 people from the right are wearing hats.
P1, P2, P3, P4 wear hat and the remaining P5 till P10 doesn’t wear hat. Let P10 be the initial sequence who doesn’t wear hat. So, the rest 5 persons wear hat - P11, P12, P13, P14, P15.
so there are 15 members.
suppose I don’t consider the sequence start as P10. First three P1,2,3 are wearing hat and P4 to P9 doesn’t wear hat. And P10, wears hat, consequently P11,p12,13,14 wears hat. So the total persons can be 14.
Hence, insufficient . statement 2:
(2) 3 of the 8 people from the left are wearing hats.
if P1,2,3 wear hat. And the remaining till 8 don’t wear hat. So either p9, or P 10 can wear a hat. Hence, we can say there were 10 people, but cannot conclusively say 10.
Hence, Insufficient Combining statements 1 and 2, we get Out of the initial 8 spots 3 can wear hat. Rest, 5 persons cannot wear hat. But question says, 4 out of 10 wears hat. This 10 can be either from left to right or vice versa.
assuming from left to right either p9 or P10 wears a hat.
statement 2 says, 5 out of 6 from right should wear hat. So if P9 doesn’t wear hat. Then , P10 to p14 wears hat. Count is 14
if we take p9 wearing hat, then we can take p8 as not wearing hat and take p10,11,12,13,14 count is. 14.
if we take p9 wearing hat, then p10 as not wearing, then p11 to p15 wears hat. Count as 15
Hence, not sufficient
Option E