JEE Main 2021 — Binomial Theorem Question with Solution
From: JEE Main 2021 (Online) 25th February Evening Shift
Question
The total number of two digit numbers 'n', such that 3n + 7n is a multiple of 10, is __________.
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Show full solutionCorrect answer: 11
Correct answer
11
Step-by-step explanation
3n = 32t = (10 1)t
= 10p + (1)t
= 10p 1
if n = even then 7n + 3n will not be multiply of 10
So if n is odd then only 7n + 3n will be multiply of 10
n = 11, 13, 15, ..........., 99
Ans : 45
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