NIMCET 2010
How many numbers from 1 to 100 are divisible by 8 and have at least one digit equal to 8?
Answer (Detailed Solution Below)View answer ā¾Hide ā“
Answer: Option A ā Four
Detailed Solution
Multiples of 8 up to 100: 8, 16, 24, 32, 40, 48, 56, 64, 72, 80, 88, 96.
Those containing the digit 8: 8, 48, 80, 88, i.e. four numbers.
ā Check
Multiples ending in 8 are 8, 48, 88 and those starting with 8 are 80, 88; 88 is counted once, giving 4.ā Common trap
(D) Six adds 18 and 28 because they contain 8, but 18 and 28 are not multiples of 8.Quick tip
List the 12 multiples of 8 and keep those containing the digit 8.
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Number System ā Preparation
This question tests your understanding of Number System, a key topic in the Quantitative Aptitude section. The detailed solution above uses a step-by-step approach to show the reasoning, and where available, a shortcut that helps you solve similar questions in under 90 seconds during the actual exam.
The number system is the foundation of quantitative aptitude. It covers the different types of numbers (natural numbers, whole numbers, integers, rational and irrational numbers, primes and composites) and the rules that govern them. Exam questions test divisibility rules, unit digits of large powers, remainders, factors and multiples, HCF and LCM, and the number of trailing zeros in a factorial. Most of these questions can be solved in under a minute once you know the pattern. Unit digits repeat in cycles of four, and divisibility by 11 depends on the difference between the sums of alternate digits. Number properties also appear inside questions on simplification, averages and series, so strong basics here save time across the whole quant section. Practise the questions below to build speed with divisibility, remainders, unit digits and HCF-LCM. Every question has a step-by-step solution and, where possible, a shortcut method.