Making Maths Count

Maths Week Scotland 2019 – Sums

October 2, 2019 by John Swinney MSP 3 Comments | Category Education, Games, Maths

Puzzle 3: Sums (almost) without Adding

If the first ten positive whole numbers are added, the sum is 55. Check it for yourself!

Use this information to find quick ways to sum the:

a)  whole numbers from 11 to 20

b)  first ten even numbers

c)  first ten odd numbers

d)  first twenty whole numbers

e)  first twenty multiples of 3

Solutions to Puzzle 3:

Answers a) 155  b) 110  c) 100  d) 210  e) 630

Tags: John Swinney, Maths Week

Comments

• SMacD says:

  October 2, 2019 at 12:43 pm

  11-20 = 155 not 165 as James O’Reilly says

  Reply
• Sonia MacD says:

  October 2, 2019 at 12:39 pm

  a) if 1-10 = 55
  Then 11-20 = 55 + 10×10 = 155

  b) if 1-10 = 55 then 2-20 = 55 x 2 = 110

  c) if 1-10 = 55 then 1-19 = 55 x 2 – 10 = 100

  d) if 1-10 = 55 & 11-20 =155 (then + together) = 210

  And finally:

  e) if 1-20 = 210 then 3-60 = 210x 3 = 630

  Reply
• James O'Reilly says:

  October 2, 2019 at 9:32 am

  a) 165
  11+20 = 31, multiply by 5 (5 pairs of 31)
  b) 110
  2+20 = 22, multiply by 5 (5 pairs of 22)
  c) 100
  1+19 = 20, multiply by 5 (5 pairs of 20)
  d) 210
  100 +110
  e) 630
  3+60 = 63, multiply by 10 (10 pairs of 63)

  Reply