Question

The sum of the integers from 1 to 100 which are not divisible by 3 or 5 is (a) 2489 (b) 4735 (c) 2317 (d) 2632

Answer 1

Answer:

2632

Step-by-step explanation:

s=sum(1-100)- sum (3-99) - sum (5-100) + sum (15-90)

= 5050 - 1683 - 1050 + 315

= 2632

Answer 2

Answer:

an = a+(n-1)d

last multiple of 3 is 99

99 = 3+(n-1)3

99 = 3+3n-3

n = 99/3 = 33

there are 33 multiples of 3

sum of these are

s₃₃ = a + an

  =( 3+99)33/2 =1,683

similarly

95 = 5n

n = 95/5 = 19

s₅₅ = (5+95)55/2= 2,750

sum of both = 2,750+1,683 =4433

Step-by-step explanation: