If a number when divided by 7 gives a remainder of 4Theory: Dividend = Divisor*Quotient + RemainderLet the number be n
n -> Dividend
7 -> Divisor
a -> Quotient (Assume)
4 -> Remainders
=> n = 7*a + 4 = 7a+4
find the sum of all such two-digit numbers satisfying this conditionn = 7a + 4
To find all the two digit numbers which satisfy this condition we need to put values of a from 1 onwards such that 7a + 4 is a two digit number
a= 1, 7a + 4 = 7*1 + 4 = 11
a= 2, 7a + 4 = 7*2 + 4 = 18
a= 3, 7a + 4 = 7*3 + 4 = 25
and so on...
By now you would have realized that this will form an Arithmetic Sequence with
(
Watch this video to Learn About
Arithmetic Sequence)
First Term, a = 11
Common Difference, d = 7
Last Term, \(T_n\) = 95 (7*13 + 4)
Let's find how many such 2 digit numbers are there
Number of terms of Arithmetic Sequence (n) is given by ( (Last Term - First Term) / Common Difference) + 1
=> n = \(\frac{95-11}{7}\) + 1 = \(\frac{84}{7}\) + 1 = 12 + 1 = 13
Sum of Arithmetic Sequence, \(S_n\) is given by = Number of Terms * Mean of First and Last Term = 13 * \(\frac{11 + 95}{2}\) = 13 * \(\frac{106}{2}\) = 13 * 53 = 689
So,
Answer will be CHope it helps!
Watch the following video to learn the Basics of Remainders