but the answer is actually 4100 i added it up on a calculator and re-did it in my head and got the right answer

the way its worded n the way ur brain add's it up, it gets tricked into thinking uve added an extra 1000 on

but theres 4 1000's thats 4000

then you have

40, 30, 20, 10.... how can that make an extra 1000 when it only makes 100????

its a trick on the mind