Q31a-Tin Co

Hi Sir,
I am currently doing revision on March/June 2018 past year paper. Referred to the question a- calculate the theoretical ex rights price per share.

Question:
If equity finance is used, a 1 for 5 rights issue will be offered to existing shareholders at a 20% discount to the current ex dividend share price of $5 per share. The nominal value of the ordinary shares is $1 per share.

Answer:
[(1x$4)+(4x$5)]/5 = $4.8

Based on the ACCA’s answer, I don’t understand why the share divided by 5 instead of 6?

Thanks.