Answer:
15 students joined the radio-controlled model club
Step-by-step explanation:
The students joining the radio-controlled model club were divided into three equal groups i.e
a) Radio-controlled boat group
b) Radio-controlled car group
c) Radio-controlled airplane group
10 new students joined the Radio-controlled airplane group and the new sum of students in this group is 15.
This implies that there were 5 students in Radio-controlled airplane group before the joining of 10 new students.
In the starting, the three groups have equal number of students which means that Radio-controlled boat group, Radio-controlled car group, Radio-controlled airplane group have 5 students in each group. Thus, In the beginning there were total 15 students who joined the radio-controlled model club