Below is an instruction that describes a task. Write a response that appropriately completes the request in English. Please answer in English.

### Instruction:
John is 10 years old. His sister is twice his age. When he is 50 years old, how old will his sister be?

### Response:
His sister is 10*2= <<10*2=20>>20 years old
Their age difference is 20-10= <<20-10=10>>10 years
Therefore when he is 50 she will be 50+10= <<60=60>>60 years old.
#### 60