Question

What is the sum of all 2- digit numbers that give a remainder of 3 when they are divided by 7 ? Select one: a. 777 b. 683 c. 676 d. 666

Answer 1

let the function be x and 0 < x ≤ 99 (2-digit)

∴ f(x) = 7x + 3

when x=1; f(1) = 7(1) + 3 = 7 + 3 = 10

x=2; f(2) = 7(2) + 3 = 14 + 3 = 17

x=3; f(3) = ... = 24

Therefore, it is an Arithmetic Progression (AP)

Using the formula:

Sn = n/2( a + l )

S13 = 6.5( 10 + 94 )

      = 6.5 (104)

      = 676

∴The answer is c. 676