Peter had some stickers. He gave half of them and an additional 60 stickers to Samuel. Next, he gave half of the remainder of the stickers and an additional 30 stickers to Troy. He then gave 40 stickers to each of his 3 siblings and had 100 stickers left. How many stickers did Peter have at first? Answer : ___

1. Calculate the number of stickers Peter had before giving to his 3 siblings.

Stickers given to siblings = $3 \times 40 = 120$
Stickers before giving to siblings = $100 + 120 = 220$

2. Work backwards to find the remainder after giving stickers to Samuel.

Before giving to Troy, Peter gave half of the remainder and an additional 30 stickers. So the amount before giving to Troy (which is the remainder after Samuel) is:
$\text{Half of remainder} = 220 + 30 = 250$
$\text{Remainder after Samuel} = 250 \times 2 = 500$

3. Work backwards to find the initial number of stickers.

Before giving to Samuel, Peter gave half of his initial stickers and an additional 60 stickers. So the initial amount is:
$\text{Half of initial} = 500 + 60 = 560$
$\text{Initial amount} = 560 \times 2 = 1120$