Remainder riddle questions ask which number leaves the same remainder when divided by two different divisors. The reliable method is to divide each option by both numbers and compare the two remainders.
For students who know division, but get stuck using remainders as clues to identify the hidden number.
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Remainder riddle questions ask you to identify an unknown number based on the remainders left when dividing by different numbers. Solving them requires testing multiples and eliminating options systematically. Here is a worked example.
Question: Which number has the same remainder when divided by 3 and 9?
Options: A. 12 B. 48 C. 17 D. 19
Step 1: Test 19 with 3: 19 = 3 × 6 + 1, so the remainder is 1.
Step 2: Test 19 with 9: 19 = 9 × 2 + 1, so the remainder is also 1.
Step 3: The remainders match.
Answer: D
To solve remainder riddles like the example above, test candidate numbers against each divisor in order. Follow these three rules:
Check each option against both divisors. To find a remainder, subtract the largest multiple of the divisor that does not exceed the number. The remainder must be non-negative and smaller than the divisor.
Example: 19 = 3 × 6 + 1, so dividing 19 by 3 leaves remainder 1.
The quotient does not need to match. Only the leftover amount matters.
Example: 19 = 3 × 6 + 1 and 19 = 9 × 2 + 1. The quotients are 6 and 2, but both remainders are 1.
If a number divides exactly by both divisors, the remainder is 0 for both.
Example: 10 divided by 2 and 5 leaves remainder 0.
A number may be divisible by one divisor but still fail the other remainder check.
Example: 12 leaves remainder 0 when divided by 3, but remainder 3 when divided by 9. The remainders do not match.
Here are two more examples showing how to handle exact division clues and test every condition thoroughly.
Question: Which number has the same remainder when divided by 2 and 5?
Options: A. 29 B. 19 C. 23 D. 10
Step 1: 10 divided by 2 leaves no remainder.
Step 2: 10 divided by 5 also leaves no remainder.
Step 3: Both remainders are 0, so they match.
Answer: D
Question: Which number has the same remainder when divided by 6 and 7?
Options: A. 49 B. 25 C. 42 D. 33
Step 1: 42 divided by 6 leaves remainder 0.
Step 2: 42 divided by 7 also leaves remainder 0.
Step 3: Both remainders match, so 42 works.
Answer: C. The trap: 49 is divisible by 7, but 49 divided by 6 leaves remainder 1.