Two successive increases of 10% [an increase of 21%]:
1 − 4/15 − 5/12 [19/60]:
I did: 4/15 + 5/12 (→ 41/60). Then: 1 - 41/60 (→ 19/60).
Or: 1 - 4/15 (→ 11/15). Then: 11/15 - 5/12 (→ 19/60).