Answer:
Step-by-step explanation:
You do not need to where the formula comes from but, just for fun, here’s a hint
To add up the numbers 1 to 10
Write out the numbers
1 2 3 4 5 6 7 8 9 10
Write them backwards
10 9 8 7 6 5 4 3 2 1
Add up both lists
11 11 11 11 11 11 11 11 11 11
This is 10 × 11 = 110
But this is twice the sum as two lots were added together
So the sum of the numbers 1 to 10 is 110 ÷ 2 = 55
ArSeqSum Notes fig4, downloadable IGCSE & GCSE Maths revision notes
