All solutions here are SUGGESTED. Mr. Teng will hold no liability for any errors. Comments are entirely personal opinions.
Let X denote the number of red sweets in a small packet of 10 sweets.
Let Y denote the number of red sweets in a large packet of 100 sweets.
Since n is large,
by continuity correction
Let W denote the number of packets out of 15 packets that contain at least 30 red sweets.