Problems on H.C.F and L.C.M - General Questions

Three bells toll at intervals of 4, 5, 10 minutes. If they toll together now, after how many minutes will they next toll together?

Three bells toll at intervals of 15, 20, 10 minutes. If they toll together now, after how many minutes will they next toll together?

Find the H.C.F. of 126, 84 and 168.

Find the L.C.M. of 5, 31 and 26.

Find the H.C.F. of 115, 138 and 161.