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How many such pairs of digits are there in the number ‘289342917’, each of which has as many digits between them in the number (both forward and backward direction) as they have between them in the Numeric Series?
One
Two
Three
Four
More than four
Let’s break it down:
- The problem wants the number of digit pairs from ‘289342917’ where the count of digits between them (both directions) matches their difference in the numeric sequence.
- For example, in '289342917', look at the pair 2 & 4. 2 appears at the start, 4 a few places later. There are two digits between them in the number (8,9), and 4-2 = 2 in actual numbers. That counts as one pair.
- You have to check every possible pair forward and backward.
Let’s test each option’s reasoning:
1. One: This would mean only one such pair matches the criteria. But with a 9-digit number, that’s unlikely—there are lots of pair possibilities.
2. Two: Same thing, feels too few. Let's look for more.
3. Three: Still feels light, but let's check.
4. Four: You picked this. Let’s count:
Actual pairs:
- (2,4): 2 between (2-4 positions: 1-4, in index terms, and numbers between) ˜ Yes, matches.
- (4,7): 2 between (indexes 4 and 7; 5 & 6 in between), number difference 7-4 = 3, but actually, that's three between—check.
- (3,9): 5 between, but 9-3=6, so that's not a match.
- (4,2): reverse, positions 4 and 8, difference 2, distance 3, so doesn’t match.
- Actually, instead of guessing, let's list all possible winning pairs via checking all arrangements.
Pairs that fit:
- (2,4): 2 positioned apart, number difference 2.
- (3,7): 3-4-2-9-1, so 3 and 7 are at indices 3 and 7, three between, number difference 7-3=4, but there are 3 between, so not a match.
- (4,7): positions 4 and 7, two digits between (indices 4 and 7, digits at 5 and 6 in between), number difference 7-4=3, so only if it's 3 between.
- (9,1): 9 and 1 at indices 5 and 8, two between, but 9-1=8.
Turns out, upon checking closely,
- (2,9): positions 1 and 5, three between (8,9,3,4), number difference 9-2=7, so doesn’t fit.
- (8,2): positions 2 and 8, five between (9,3,4,2,9), number difference 8-2=6, nope.
So, false starts. What this really means is: There are only actually two pairs that fit the rule:
- (2,4): positions 1 and 4. Two in between, 4-2=2.
- (9,7): positions 5 and 7. One between (index 6), 9-7=2. But there’s only one between.
Let’s check if we missed one. Try (4,2):
- Indices 4 and 8, three between; 4-2=2, so doesn’t fit.
Basically, only two pairs actually work.
So the correct answer is:
Option:2, Two
Here’s what to remember:
- Go digit by digit, both left to right and right to left.
- Compare the digit difference with the number of spaces between them.
- Only two unique pairs fit that rule here.
There you go—next time, sketch the nine digits, and run those test pairs line by line to avoid guessing.
By: Parvesh Mehta ProfileResourcesReport error
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